Many ponds in central Illinois are very green this time of year with high populations of floating mats composed of filamentous algae. On close inspection, filamentous algae look like green hair, and the floating mats are formed by hundreds or thousands of these strands.

I have received a number of phone calls regarding control or removal of this vegetation. Summer algae control is complicated, because high water temperatures affect the available dissolved oxygen to fish and other aquatic organisms. The Illinois Department of Natural Resources uses July 1^st as a recommended cut off date for whole pond herbicide applications. Partial control of aquatic vegetation is still an option, but care must be taken not to dramatically increase the oxygen demand in the pond.

If aquatic vegetation, including algae is killed during the late summer months their decomposition uses oxygen, and combined with the lower oxygen holding capacity of warmer pond water can sometimes lead to a fish kill. These late summer conditions leave pond owners with two options for algae control: first tolerate the algae, or secondly apply herbicide to only a portion of the aquatic vegetation.

The first option has some obvious drawbacks. High populations of algae reduce aesthetics and decrease the quality of the pond for swimming and boating. However, tolerating the algae is probably the safest management option for planktonic algae blooms in late August and early September. The entire pond must be treated with an algaecide to control planktonic algae.

Filamentous algae are more practical to kill with a partial pond treatment. The floating mats of filamentous algae can be sprayed, but no more than one-fourth of the vegetation should be killed at one time. At least seven to ten days should be allowed between applications to allow decomposition, and then another portion of the vegetation could be treated.

Remember that even partial herbicide applications will reduce available oxygen levels. Therefore, the condition of your pond and weather conditions should be carefully evaluated before making the application. Also keep in mind that cooler air and water temperatures in September will slow down the growth of the vegetation naturally.

The University of Illinois Champaign Extension Unit will host a Twilight Pond Walk to help you better understand your aquatic resource on September 22^nd, from 6:00 to 8:00 pm. The workshop is a result of a collaborative effort between the Champaign County Soil and Water Conservation District, the Urbana Park District and the University of Illinois Champaign Extension Unit.

The workshop will begin at the boat house in Crystal Lake Park, located off Broadway Avenue in Urbana at 6:00pm. Dave Shiley, U of I Extension, will present information, during a walking tour around portions of Crystal Lake, on fisheries management through the use of creel surveys, journaling and harvesting. Nuisance wildlife management and vegetation management issues will also be discussed. Bruce Stikkers, Champaign County Soil and Water Conservation District will provide information regarding shoreline management and watershed management techniques.

Please dress appropriately, as we will be standing and walking during a portion of the seminar. For more information contact the University of Illinois Champaign Extension Unit at 217-333-7672.

There is a $10 per person fee for this workshop. Register online.