How do streams and lakes compare (WSA to NLA)?
Stream and lake condition as described in the Wadeable Streams Assessment (WSA) and the National Lakes Assessment are not entirely comparable because different indicators of biological condition were used. In the NLA, EPA used a taxa loss model based on planktonic communities as the indicator of overall condition. In the WSA, EPA assessed the overall condition of streams using an index of biological integrity based on benthic macroinvertebrates. Nationally, the WSA showed that 42% of our nation’s stream length is in poor biological condition relative to the least disturbed reference condition. This contrasts with NLA findings of only 24% of lakes in poor biological condition. However, it can be noted that both assessments found that nutrients and poor habitat conditions were leading stressors and posed the highest risk to good biological health.
