(CN) - Toxic chemicals from sewage and fertilizer runoffs are damaging U.S. coastal waters and Great Lakes, and the contaminants are creeping up the food chain into fish tissue, federal scientists said.
A water quality assessment conducted by the U.S. Environmental Protection Agency (EPA) found a potential threat to fish-eating species in 99 percent of waters surveyed.
Scientists claim the largest contributors to poor water and ecological quality are high levels of phosphorous and selenium from human sources.
Excessive amounts of phosphorous in watersheds can cause harmful algae blooms known as red tides, while high selenium levels are known to mutate fish and birds.
Selenium contamination has been connected to two-headed trout in Idaho and wingless birds in California's Central Valley, according to an NPR report.
EPA researchers sampled more than 1,100 coastal and Great Lakes sites in the summer of 2010 as part of the agency's National Aquatic Resource Survey program. The EPA survey is the first to examine the shore waters of the Great Lakes in a probability-based survey.
According to the data, all 157 fish samples from the Great Lakes contained detectable levels of contaminants. Each of the Great Lakes currently has government warnings regarding fish consumption.
Joel Beauvais, EPA deputy assistant water administrator, said with more than half of the country's population living close to coastal waters, it's important for scientists to continue studying the fragile habitats.
"The latest science confirms we must keep paying close attention to our coastal waters, reduce the pollutants that are harming water quality and protect those areas still in good condition," Beauvais said in a statement.
The study indicated that the contaminants could have negative long-term effects on fish-eating species but it did not evaluate the potential human health risks.
A recent study of blood mercury levels in birds eating fish from contaminated lakes in California found grebe species at risk for reproductive problems. The grebes were used as indicators for the contaminant study because they are near the top of the lake food chain and feed primarily on fish.
While ecological fish tissue quality rated poorly in the EPA study, water quality graded much higher. Scientists found good water quality in 36 percent of areas sampled and fair quality in 48 percent.
Sediment quality also graded highly as 79 percent of coastal waters were found to have low levels of sediment contaminants. Sediment contamination occurs when chemicals accumulate on the bottom of a body of water and areas near mining operations, for example, are notorious for high sediment contamination.
Since the last EPA coastal survey in 2005, overall water quality remained essentially the same, according to the 129-page report.