August 2013



Q: What causes many lakes, rivers and ponds to turn green by mid-summer? Some even have an odor.

A: By mid-summer many waterbodies turn green due to the growth of small microscopic plants in the water called algae. Algae grow in all bodies of water when light and nutrients levels are sufficient.

In many lakes, algae abundance is determined by the amount of phosphorus dissolved in the water. The more phosphorus present, the more abundant algae become and the greener the water gets.

There are many different types of algae. During mid-summer one particular group of algae, called blue-green algae, are often particularly abundant. When this algal group becomes abundant, a strong musty or earthy odor many occur. Algae that have died and are decomposing cause the odor. Because algae abundance strongly depends on the amount of phosphorus available, the best long-term strategy is to improve land-use practices to prevent phosphorus and other nutrients from getting into our lakes and ponds.

- Dave Wright, DNR lakes and rivers unit supervisor


Q: The DNR is in the process of determining the abundance of pheasants in the state's pheasant range. How is this number determined?

A: Since 1955, the Minnesota DNR has conducted annual roadside surveys during the first two weeks of August to estimate pheasant abundance. These surveys entail counting all pheasants observed while driving each of 152 survey routes – one to four routes per county – in Minnesota’s pheasant range. DNR wildlife staff survey these 25-mile long routes in the early mornings on days with clear skies, light winds, and heavy dew. Because pheasants are difficult to count, techniques used to determine population estimates for other wildlife species do not work with pheasants. Thus, the annual August roadside surveys do not provide a total census, but rather an index of relative abundance. This information is then used to monitor changes in the pheasant population over time.


- Nicole Davros, DNR wildlife biologist







-Val Cervenka, forest health program coordinator, DNR Forestry Division





DNR Question of the Week Archive