Tyler Chalfant | November 14th, 2019

The Iowa Department of Natural Resources found that the number of polluted lakes, rivers, and streams in the state continued to rise in 2018. The DNR has compiled a list of lakes, rivers, streams and wetlands that fail to meet water quality standards every other year since 1998. This failure can result from pollutants including, high amounts of bacteria, harmful algae, low oxygen, or high levels of mercury in fish.

Since 1998, the number of impairments on the list has grown every two years. However, officials caution against using these numbers to interpret long-term trends, as methodology changes over time, and each year’s report includes data for the previous five years as well. The most recent survey found 1,110 impairments on 767 freshwater segments, compared to 1,096 impairments on 750 segments in 2016. 

Not every freshwater body is monitored, but of those that were, a majority of lakes and reservoirs, as well as rivers and streams, were found to be impaired. Bacteria was found to be the most prevalent cause of impairment in rivers and streams, while algal growth was the most common in lakes, reservoirs, and wetlands Overgrowth of toxic blue-green algae, which can result from nutrient runoff, was especially prevalent this summer, and Lake Macbride had its first-ever swim advisory in July.