| Story by Meghan McMahon |
What lies beneath the water’s surface is a mystery to most of us, but it’s teeming with life down there. Our lakes, ponds, rivers, streams and wetlands are filled with all manner of creatures, from microscopic zooplankton and crustaceans to mollusks and, of course, fish.
And the diversity of freshwater fish is impressive. Although 97 percent of the water on Earth is salt water, more than half of all fish species — 51 percent — live in fresh water, according to the World Wildlife Fund. The world is home to more than 18,000 species of freshwater fish, accounting for a quarter of all vertebrate species in the world. Research shows, however, that almost one-third of freshwater fish species are threatened with extinction.
But extinction isn’t just a threat; it’s already happening. Sixteen freshwater fish were declared extinct in 2020, according to the wildlife fund. And freshwater fish have declined in population by 76 percent since 1970; megafish — defined as those that weigh more than 66 pounds — have seen their numbers drop by 94 percent in the same period.
Freshwater fish are just one essential component of Earth’s freshwater ecosystems, which include the planet’s lakes, ponds, rivers, streams and wetlands. In the midst of a biodiversity crisis across the planet, our freshwater ecosystems are particularly imperiled. The population of all freshwater species have declined by an astonishing 84 percent, and almost a third of our wetland ecosystems have been lost since 1970, according to Conservation International.
The degradation of freshwater ecosystems and the decline in water quality is mostly caused by human activity, the wildlife fund reports. Invasive species — often inadvertently introduced by humans — and overfishing have devastating effects on freshwater fish populations. Other human-caused threats include climate change, because fish do not tolerate temperature change well, as well as pollution and improper and poorly constructed dams that alter the natural hydrology of an area.