Humans Are Accelerating Extinction of Freshwater Fish

Freshwater species are more threatened than terrestrial or marine wildlife, and each of us can stop it with our choices and behavior.

Julie Smith, 5/6/26

This is a summary of Chapter 10, Freshwater Wildlife, in the book, “2050: What’s it Gonna Be?”.  You can download the full chapter, as well as other chapters.  References are here.

90% of fresh water ecosystems are being stressed by pollution, dam building and invasive species.  The freshwater wildlife lives in the continental creeks, streams, rivers and lakes of our planet, with completely different lifestyles and issues, compared to the marine life.  Since fresh water bodies are generally smaller than seas, with the exception of extremely large lakes, such as the great lakes, freshwater species are more entwined with wildlife that lives on land, that depends on them for an important protein source.  Also, land wildlife has to live with the same water impacts that freshwater species have to live in.

In the past 50 years, while global wildlife has declined by 60%, the greatest losses have been with freshwater wildlife.  Freshwater fish make up more than half of global fish species, yet fresh water is only about 1% of the total aquatic habitat.  Global warming, dropping water levels, pollution and overfishing have reduced freshwater fish by more than 80%,¹  and 25% of freshwater fish species are threatened with extinction.²  Is that scary or what?

So, if humans are accelerating extinction freshwater fish, how are we managing to do that?  Well, that’s easy.  Between sewer and stormwater overflows, water-borne diseases, fertilizers, insecticides and herbicides from non-point agriculture and home yards, petroleum-laced road runoff, tire fragments and litter, livestock trashing land and riverbanks with their shit running into the water, as well as logging and deforestation that increases runoff and erosion of silt into the water, and pollution from industries who choose to “cheat” on their toxic effluent discharges, it’s an absolute miracle that any life at all can live in our surface waters. 

Cyanobacteria and blue-green algae appear annually in Upper Klamath River in Oregon, and when they die, their decomposition consumes the oxygen, suffocating the fish and other organisms.  The algae also produce microcystins, neurotoxins and possible carcinogens that can’t be boiled or easily filtered out of the water.  Swimming in it can cause rashes, and ingesting it can cause kidney failure in humans, and sicken or kill dogs and wildlife.

We’ve also created barriers and restrictions to natural movement and migration through waterways, most notably with dams.  Urbanization threatens biodiversity in streams, because of extensive stream degradation.  We’ve bulldozed rivers, turned them into unnaturally straight aqueducts, paved riversides and built homes next to rivers and lakes.  All of this causes pollution in the waterways, and adds noise and light stress to the aquatic ecosystems.

And, naturally, global warming plays a huge role, warming waters to the point that fish can’t live in it, sort of like how people in Phoenix can’t live in 100+ ºF heat without air conditioning.  Except the fish don’t have air conditioning, so they simply die of heat stroke unless they can migrate to cooler water.  Also, warmer water holds less oxygen, which the fish need to breathe, so that can’t be helping things.  The warm water stresses them and increases disease.  And some diseases are just as bad for us as they are for the fish.  Like brain-eating amoeba, now showing up in warmer waters.  A Nevada boy died recently from it after swimming in Lake Mead.⁵

Also, as with every other species on the planet, overfishing is playing a huge role.  Steelhead trout, for instance, once numbered 15 million in the Columbia River Basin, and overfishing had dropped it by more than 99%, down to 100,000 by the late 90’s.  There has been a little recovery since then, up to around 350,000, but that’s still only 2.3% of the original population.  And, it’s unlikely that they’ll ever reach anywhere near their original population as long as the water keeps warming.

24,000 dead menhaden were discovered in Baltimore Harbor, as a result of the severe environmental challenges facing Chesapeake Bay.  The cause of the fish kill was a thermal inversion made worse by nutrient-rich stormwater runoff, pollution and rising water temperatures, which continue to degrade water quality and harm aquatic species.

The industrial agriculture waste that has created the dead zone in the Gulf of Mexico is carried into the gulf by rivers from the midwestern and southern U.S. megafarms.  The dead zone itself is more than 6,000 square miles, so you know a lot of nutrients and toxins are being carried in those rivers.  And it follows that those rivers are too toxic for any wildlife, so that takes care of freshwater fish and wildlife in pretty much a third of the U.S.  And each and every one of us can help this by only buying organic food.  And recovering the extra cost of the organic food by not wasting any of it.  And sticking with vegetables rather than meat and dairy, which is more expensive than vegetables.  How hard can it be?

Wetlands are home to an amazing array of wildlife species that depend on them, from fish to insects to birds to terrestrial wildlife.  For birds throughout the world, they provide extremely important layovers on migration routes.  They are also extremely powerful carbon sinks, they purify water that flows into larger water bodies, like lakes, by literally removing nutrients from agricultural runoff, and they provide buffers that control flooding and help prevent erosion.  Even though they only make up less than 4% of the planet’s surface, they’re a key factor in the future of our climate.  Globally, wetlands generate about $49 trillion in economic benefits per year for all of these services.

Yet, as always, we find reasons to drain them and ruin them with coastal development, dumping our trash, draining them for agriculture, and depleting water supplies to them as our constantly growing populations demand more and more water.  Agriculture for our food is the biggest driver of draining wetlands, and globally we’ve lost 35% of our wetlands in the past 50 years.¹²  A disproportionately huge part of agriculture is feed for cattle. In the past century, we’ve removed half the original wetlands in the U.S., and in California and New Zealand they’ve lost a whopping 90%. 

Along the Southeast U.S. coastline, extensive development is whittling away at the marshes, and efforts to restrict coastal development are blocked by laws that prevent regulators from restricting development.  It’s not helping that U.S. policymakers continue to fight natural waterflows and flooding with flood-control projects that disrupt the flow of rivers and encourage development in floodplains.

We continue to make the situation worse, even though increasing wetland coverage by just 10% would cut nitrate levels in rivers and streams by as much as half, and nutrient pollution would be far worse without the wetlands that we still have.  In Uganda the government is showing some level of common sense, and has suspended all development in the country’s wetlands in an effort to preserve them. 

The Amazon is losing wildlife and freshwater species just like everywhere else, as it gets habitat destroyed for agriculture, and overpopulation leading to overfishing.  Global warming is taking a huge toll, with record high temperatures of 102 ºF in the Amazonia lake killing record numbers of the much-loved pink river dolphins. 157 dolphins croaked in just a few days, amounting to about 10% of the lake’s population.¹⁸  At that rate, in addition to the overfishing and poisoned water, it doesn’t sound like river dolphins are long for it.

Each of us humans can stop the acceleration of extinction of freshwater fish with simple everyday choices. Eat Organic. Never waste food. Don't eat beef and dairy. Don't use toxic cleaning or personal care products. Minimize or eliminate single-use paper and cardboard, and always recycle what can't be avoided. Advocate against developments near water bodies or wetlands. Reduce energy consumption and move to all-electric homes and vehicles, fueled by renewables. Support human population reduction.