WASHINGTON, Aug. 13 (UPI) -- The rate at which freshwater fish species in North America go extinct may double within 40 years, a study from the U.S. Geological Survey says.
The USGS, in a study set for publication in the September issue of the journal BioScience, says North America lost 39 species of freshwater fish from 1898-2006, based on fossil records. As many as 86 species of freshwater fish may be extinct by 2050, however.
The USGS report finds that extinction rates for freshwater fish could be overshadowed by long-term trends for mussels and snails.
Recent fish die-offs were attributed to the record-setting heat wave that gripped much of the U.S. Midwest this summer. Sections of the Des Moines River reached 97 degrees Fahrenheit, decreasing oxygen levels for marine life.
Scientists working for the National Aeronautics and Space Administration said that extreme weather events like this year's heat wave can't be explained by natural phenomena alone.
"The accelerated pace of extinction observed since the beginning of the twentieth century suggests human causes," as USGS summary of the report on freshwater fish stated.
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