MINNEAPOLIS – Many urban streams have become salty enough to harm aquatic life, largely because of salt used for deicing roads in the winter, according to a new government study released Wednesday.

The U.S. Geological Survey studied urban streams and groundwater for levels of chloride, a component of salt, in 20 states spanning from Alaska to the Great Lakes and Northeast.

It found chloride concentrations above federal recommendations designed to protect aquatic life in more than 40 percent of urban streams tested. The highest levels were measured in those streams during the winter – as much as 20 times the federal guidelines – when salt and other chemicals are commonly used for deicing.

The problem was less serious in groundwater, and fewer than 2 percent of the drinking-water wells sampled had chloride levels higher than federal standards for human consumption. Chloride levels generally were much higher in urban than rural areas.

High chloride levels can slow plant growth, impair reproduction and reduce the diversity of organisms in affected waters. It also can affect the taste of drinking water drawn from them.

Some of the highest concentrations of chloride were found in two creeks in the Twin Cities and four creeks in suburban Chicago, but Lincoln Creek in Milwaukee exceeded the federal guidelines the most out of all the streams cited in the study.