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Science & NatureGreen TalkAre freshwater fish at risk?

Are freshwater fish at risk?

by Theresa Peluso

Why are freshwater fish important – and are they at risk?

I would like to preface this column with an account written by a former resident of Mississippi Mills:

The Mississippi River – A “Fish Story”

By Alan Todd

Framed by a pastoral Lanark County, the quiet dark flow of the ancient Mississippi River slides by beneath willow bough and evening. The water view from my historic island home above the rapids on Glen Isle seemed complete; within reach a slow-moving pool alive with countless shining smallmouth bass; airborne, feeding, showing off, all playful jokers rising and falling swallowed by brilliant watery circles drawn in a surface of fading light. Then, not

a moment passed when the water was still, and in this swirl a natural harmony of connection seemed evident in all…. It seemed sudden, even after seventeen years as an observer in this environment, when it became apparent that there was a profound decline in fish numbers. This wild place was now transformed; not one fish could be seen where there were hundreds, and in the process my idyllic life on the island would lose its great context. The real nature of the river to the common eye had not changed, but in the practice of agriculture and habitat destruction the change was inevitable; it was preventable but beyond our willingness to understand and act in defence of a world out of sight. This separation between nature and society; this dislocation, prevents us from acknowledging the effects of loss.

Alan Todd and his family left their home on Glen Isle in August of 1987. Alan has a renewed sense of good stewardship and is currently volunteering with Ottawa Riverkeeper.

Quoted in the Ottawa Riverkeepers River Report, May 2006, Issue 1:  Ecology and Impacts

As I mentioned in my previous column on fish, there are several differences between marine and freshwater fish, apart from their habitat, which explains why the topic of the importance of fish to the environment has been divided accordingly.

First, the physiological differences. Because marine fish lose water through their skin and gills as a result of their saltier environment drawing water from their body tissues, marine fish compensate for this dehydration by drinking large quantities of saltwater, producing little urine, and secreting the excess salt through their gills.  In contrast, freshwater fish don’t experience dehydration, and therefore have no need to drink additional water.  They also produce large amounts of urine.  Secondly, quite apart from the presence of salt or lack thereof, marine and freshwater environments differ in the amount of change they undergo (with respect to temperature, salinity, ammonia, nitrate and pH levels).  These changes are significantly greater for freshwater fish.

Freshwater fish, which comprise approximately 40 percent of all fish species, and 20 percent of all vertebrate species, are a significant element of our web of life.  Consider that the total volume of water on Earth is estimated at 1.386 billion km³, with 97.5 percent being salt water and 2.5 percent being fresh water.  Of this fresh water, only 0.3 percent is in liquid form on the surface.  So 40 percent of all fish species live in approximately 103,950 km3 of the Earth’s water.

Freshwater fish are the sixth major supplier of animal protein to humans globally.  In some countries, especially less developed ones, they supply over half of the population’s animal protein, and are a source of employment for millions of the world’s poorest people.  Globally, freshwater contributes over 40 percent of the worlds’ reported finfish production.  Keep in mind that, according to the IUCN FFSG (International Union for Conservation of Nature:  Freshwater Fish Specialist Group), there is a 221 percent discrepancy between official yield figures for freshwater fish and the estimated consumption.  Officially, 1.2 million tonnes are consumed; actual estimates are more in the range of 2.6 million tonnes.

In our province, people depend far less on these fish for protein, but recreational fishing contributes over $2 billion per year to Ontario’s economy, and attracts over 1 million anglers each year.  This doesn’t include the economic value they contribute to tourist activities like diving and snorkelling, and to aquarium-keeping.  Apparently, the global economic value of aquarium-keeping is in the neighbourhood of $15-30 billion U.S.

In addition to their importance as a source of food for people and their economic benefits, freshwater fish are an integral part of our ecosystem. Freshwater fish, like their salt-water counterparts, regulate the food-web dynamics.  As fish go through their various life stages, they serve as food for other organisms, or process other organisms in their environment. For example, they influence the availability of nutrients and the potential for algal blooms in nutrient-rich lakes, by ingesting nitrogen and phosphorus and then excreting these elements in a form that primary organisms can absorb.  Freshwater fish also stir up nutrients in the lake or river bed, and transport them to the upper layers, making them available to other organisms within the lake or river.  As a result of their daily, seasonal and yearly migration patterns, freshwater fish serve as active links between ecosystems.  A perfect illustration of this is the coho salmon, which are a food source for 22 species of mammals and birds living near the river.

Fish communities are excellent indicators of the water quality of rivers and lakes because they are continuously exposed to it.   Changes in their appearance, growth, distribution and abundance provide evidence to researchers of the impacts on our aquatic ecosystems. Furthermore, the immense diversity of freshwater fish species confers the benefit of adaptability in the event of disturbances to our ecosystem; for example, droughts, severe storms, and diseases.  The study of fish has also enabled researchers to develop advances in biotechnology and medicine.  Fish also play an important part in the customs and art of many cultures.

Despite the important role freshwater fish play in human survival, culture and environmental sustainability, very few countries are providing them with the necessary protection.  What is the situation in our country?

In a 2017 report titled Freshwater at risk, by World Wildlife Fund Canada (WWF-Canada) (, 25 watersheds in Canada are assessed. This study has identified significant disturbances to freshwater ecosystems from human activities such as pollution, agricultural runoff, habitat loss, climate change, oil and gas development and hydropower dams.  On top of these existing problems, new technologies and practices are likely to contribute even more new pollutants and stresses to our freshwater systems.

Despite the fact that our country doesn’t collect enough data to know just how extensive this damage is, the researchers of this report have ascertained that almost two-thirds of the subwatersheds in Canada have fair or poor water quality.  In our country, home to 20 percent of the global endowment of freshwater, wildlife populations in these waters have declined by 81 percent over the last 40 years.  We, as a country, are clearly not doing our part, and must pressure our federal and provincial governments to increase their investments in researching, monitoring, and protecting our freshwater systems.

Another, more local, source of information on freshwater fish is the 2006 Ottawa Riverkeepers River Report, cited above. At the time this report was prepared, the Ottawa River was home to 96 species of fish, including the lake sturgeon, a migratory fish.  In 1953, a 154-year-old, 94.6-kg specimen was caught in Lake of the Woods.  Owing to uncontrolled commercial harvesting and changes to its habitat, the population of lake sturgeon declined, and in 2006 was less than 1 percent of historical levels.  The good news is that, thanks to recent conservation efforts, this species now seems to be rebounding.

One threat to fish living in the Ottawa River, like the lake sturgeon, is that this river is one of the most highly regulated Canada, with over 50 major dams and hydroelectric generating stations. On the Mississippi River alone there are over 30 water-control structures.  Although run-of-river dams generally have fewer impacts than those with significant reservoirs, some dams, such as the Enerdu generating station, stretch the rules by artificially maintaining higher-than-normal water levels.

Damming water upstream removes the river’s natural rapids and pools with flat-water reservoirs, eliminating valuable habitat for those species adapted to fast-moving water.  Furthermore, rapids are the “lungs” of the river, because the turbulence traps air in the water, which eventually gets dissolved – a little like a large-scale aquarium pump. Reservoirs have been shown to have dramatic effects on temperature, nutrients and dissolved oxygen, accelerating decomposition, and generating toxic compounds such as methylmercury.  In addition, barriers such as flashboards and gates result in fluctuating water levels, and contribute additional stresses to aquatic life. Even run-of-river dams can interfere with the movement of fish and water, although to a lesser extent than major hydro-electric dams. According to a Parks Canada study, populations of the American eel, another once abundant migratory fish like the sturgeon, have declined 99 percent in recent years, largely because of obstructions like hydroelectric turbines. Encouraging hydro-electric stations to incorporate conservation measures; for example, eel ladders, as Ontario Power Generation is doing, can help to alleviate some of the impacts of dams on fish.

And now, the problem of water pollution. Here is another quote from the 2006 Ottawa Riverkeepers report: “At one time you could scoop water from almost any location in the river and drink without a worry. Today most cottagers, canoeists, and shoreline residents treat their river water before drinking it.”

The problem of municipal wastewater effluent entering our rivers and lakes is a significant source of contamination of our freshwater.  It consists mainly of household waste such as feces, food, pharmaceuticals, cleaning products, oils, grease and cosmetics.  Then there’s industrial wastewater effluent, containing metals such as mercury, arsenic, lead, chromium and cadmium, and other toxins, depending on the industry.  And finally, there’s stormwater and agricultural run-off, especially following severe storms, which contains animal waste, litter, salt, pesticides, fertilizers, rubber, de-icing agents, oil and grease.

As this wastewater enters our rivers, it triggers an increase in nutrient levels, often leading to algal blooms; depletes dissolved oxygen, sometimes resulting in fish kills; destroys habitat by covering it with sedimentation and debris; and results in poisoning the water and its denizens with chemical contaminants, either immediately, or through the bioaccumulation of chemicals at higher levels of the food chain.

At the time the Ottawa Riverkeepers 2006 report was written, in the Ottawa River watershed, there were over 90 municipal wastewater treatment facilities. Over half of the facilities provided only primary treatment, resulting in significant contamination of the river.  In an interview in 2016 with Don Butler of the Ottawa Citizen, Ottawa Riverkeeper Meredith Brown had more positive news. She reported that the volume of overflows from Ottawa’s combined sewers fell by more than 80 per cent between 2006 and 2015, mainly because of the installation of real-time controls, which allow the remote activation and control of overflow equipment and continuous monitoring to maximize the capture and treatment of waste water ( Mississippi Mills too, as of 2012, has a wastewater treatment plant to treat municipal sewage and septage.  Not all the municipalities on the Ottawa River have followed suit, and so the problem of effluent in the river continues to be a problem, although to a lesser extent. In all cases, stormwater management continues to be a concern.

As for the Outaouais-based industrial wastewater effluents discharged into the river, the pulp and paper mills use the most water and generate the most effluent. Despite decades of investments to improve the environmental performance of the pulp and paper industry, significant effects on aquatic ecosystem health continue to be documented across the country.

Especially of note are the nuclear facilities at Chalk River, which in 2012 were still discharging nuclear reactor effluent into the Ottawa River, and, despite strong objections from hundreds of experts and environmental advocates, are now proceeding to build a five-storey-high dump in a swampy area roughly a kilometer from the river for toxic and radioactive waste from the Chalk River site and from other federal nuclear sites. (See the Ottawa Riverkeepers’ assessment here: .)

Despite the steps taken by municipalities, in the last 20 years, to improve treatment of wastewater and sewage, new chemicals in our water continue to be identified.  Canadian researchers have identified numerous water-quality threats to our water, including acidification, endocrine-disrupting substances, pathogens, pesticides, and algal toxins.  Municipalities need to find ways to factor in these new threats when upgrading their facilities.  So do homeowners, by cutting down and eliminating use of toxic materials, and disposing of hazardous and medical waste appropriately.

Microplastic pollution is yet another threat.  A 2016 study conducted by the Ottawa Riverkeepers ( revealed that microplastic concentrations in the Ottawa River are similar to those reported for Great Lakes tributaries, which were found to have up to 40 microplastics, including microfibers, in their digestive tracts.  Microplastics were found at all 58 sampling sites throughout the watershed, including six tributaries which had the highest concentrations in Ottawa/Gatineau region.  Canada, on taking presidency of the G7 this year, has committed to take leadership in preventing further contamination of the planet by plastic pollution.  Let’s hope that our country takes concrete action to ban single-use plastic in our own country, and follows the example set by several other jurisdictions.

Other problems affecting the survival of freshwater fish are habitat loss, indirectly, from deforestation and drainage of wetlands; and directly, from destruction of natural shorelines.  Natural shorelines not only provide habitat for aquatic species, including fish; like wetlands and forests, they also help to maintain water quality by retaining, treating, and filtering surface pollutants and runoff before they can reach the water. Healthy shoreline vegetation and tree-planting help to prevent erosion from heavy rainfalls, waves and ice, slow the movement and speed of water downstream, and provide wildlife with food and habitat. Did you know that debris from forest cover near lakes causes fish to get “fat”?  Yet another reason to encourage tree planting near water bodies! (See Forest loss starves fish, June 11, 2014, University of Cambridge, published on the website .)

Another threat to freshwater fish is human-caused global warming, which affects our lakes and rivers in many ways.  The warmer air and water temperatures not only directly affect the flora and fauna in our lakes and rivers; they also cause more extreme weather events, such as droughts and flooding, and changes the normal duration and amounts of precipitation, which affect the amount and quality of water and other matter that drain from the tributaries into larger water bodies. Unlike marine fish, which may be able to migrate to cooler waters, freshwater fish are usually confined to certain sections of the river or to the lake where they live.  A lack of water resulting from reduced snow- or rainfall may result in these fish no longer having enough water to survive or to migrate and breed.

Because fish are cold-blooded, they can’t control their body temperature.  Warmer temperatures lead to stunted growth, reduced numbers of offspring, or inability to reproduce.  Some fish such as salmon, catfish and sturgeon can’t spawn if winter temperatures don’t drop below a crucial level. Certain endangered fish, like the river redhorse (which has been found in the Ottawa, Madawaska and Mississippi rivers, and depends on clear, unpolluted, cool water, and moderate to swift currents) may become extinct.  One exception to this is that some warmer-water fish, like smallmouth bass, are likely to increase.

Finally, there is the threat of invasive species such as zebra mussels, fungal diseases and wood-feeding insects (such as the emerald ash borer), Eurasian water milfoil and phragmites, which also degrade the habitat of fish and other aquatic animals by monopolizing their food sources and outcompeting or destroying native vegetation.

To situate the problem of threats to freshwater fish in our watershed within a global perspective, a report by the above-referenced IUCN (Reid et al., 2013). states that freshwater fishes may now be the most threatened group of vertebrates, based on more than 5,000 species assessed to date. According to the Living Planet Report 2016, a World Wildlife Fund report, freshwater species populations (including fish) dropped by 81 percent globally between 1970 and 2012, and population declines are predicted to continue.  All the threats identified in this report echo what is happening in the Ottawa River watershed.  One problem, overfishing, seems not to be a factor regarding our watershed (apart from accounts of overfishing of the American eel), and this would appear to be a result of Fisheries and Oceans Canada’s efforts to monitor, control and enforce fishing regulations, on which they spend $130,000,000 annually, making this program one of the most advanced in the world. (See the 2017 report .)

The Ottawa Riverkeepers provide several suggestions to boaters, fishermen and –women, homeowners, shoreline residents, and others, on how to protect our lakes and rivers, and the flora and fauna in them.  The recurring points are to:

  1. a) refrain from putting into the water any contaminants (fuel, pesticides, fertilizers, toxic cleaners, phosphates, sewage, etc.) and other pollutants, such as plastics, lead sinkers and jigs, and unwanted aquarium or water-plants;
  2. b) if you operate watercraft, avoid areas infested with invasive species, travel at moderate speeds to prevent damage by high wakes, and clean your vessel after each outing to prevent the transmission of invasive species to new areas;
  3. c) conserve water;
  4. d) if you own shoreline property, keep the shoreline natural and plant native species; and
  5. e) get involved and participate actively in local decisions that may impact nearby rivers or lakes, join a group that advocates for environmental protection, and take part in shoreline clean-ups and other community events that focus on the rivers or lakes.

Theoretically, in our country we might be able to survive without freshwater fish, but what would end up killing them would do us in as well. For their sake– and for ours – we must do what we can to live more sustainably.




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