DNR Response to District member inquiry

Beaver Dam Lake is a nutrient-rich, very shallow impoundment so it’s highly susceptible to blooms. There are local and regional efforts to address the nutrient pollution which is fueling the blooms, but unfortunately the lake is in a similar situation to other shallow-nutrient rich impoundments throughout Wisconsin, in that the creation of these water bodies also inadvertently created conditions that foster blue-green algal growth.

Additionally, despite recent rains, Dodge County is still in severe drought conditions. There may be lower flow rates through the lake due to the drought, so the water is warming and stagnating which intensifies blue-green bloom growth.

Unfortunately, there are not good options for dealing with blooms when they get to the level as seen in your photos. As you noted, wind direction will influence where the blooms accumulate. The blooms in your photos also appear to be in the process of breaking down and decomposing, which is why the smell is so bad.

The conditions in your photos are those that DNR and DHS recommend that people do not swim in, and pets should be kept out as well. If you have pets that eat grass, do not irrigate your lawn with lake water when blue-green algae are present.

The Wisconsin Department of Health Services has a family fact sheet and a dog fact sheet that show you the blue-green algae conditions to watch out for and to avoid. If you have very young children or dogs who will be swimming in the water, it’s safer to keep them out when floating areas of blue-green algae or discolored water are present, and always stay out when conditions resemble those in the fact sheet photos. Pay attention to wind direction too, as blooms can accumulate on downwind shores.

Local public health departments have the jurisdiction for beach monitoring in Wisconsin. You can find information about beach closures at the Wisconsin Beach Health Advisory Map or if beaches are not on that map, on local public health websites. Most local public health departments do not have the capacity for blue-green algae monitoring. Monitoring can be very challenging as blue-green algae concentrations can change very rapidly, so the best thing you can do is to learn what blue-green algae look like and assess water conditions for yourself before swimming or engaging in other water recreation:

  • Blue-green algae are in all water bodies in Wisconsin. Waters with high nutrient levels are most likely to have blooms, but even lakes with excellent water quality may experience surface blooms, especially after periods of calm weather when wind can blow blue-green algae into one area of a lake.
  • Blue-green algae can also grow on lake bottoms and rivers as mats, which sometimes float to the surface.
  • It’s always a good idea to avoid swimming in areas with a lot of tiny particles in the water, opaque “pea soup” water, or dark-colored floating mats. All of these may be blue-green algae. Always avoid swallowing untreated surface water because it may contain bacteria, viruses, and parasites that could make you sick.
  • If small children and dogs are swimming, choose the clearest water possible for them to swim in.
  • Don’t let dogs swim or play in shallow, stagnant areas where blue-green algae mats may be growing on the bottom and dislodged by disturbance.
  • Don’t let dogs eat floating material in the water, or material washed up on shore.
  • In dogs, water intoxication (from swallowing too much water) and heat stroke share symptoms with blue-green algae poisoning. Give dogs plenty of breaks from playing and retrieving in lakes and give them flat objects for retrieval instead of balls. Always provide shade and fresh, clean water to drink, and wash them off with clean water after they swim, so they don’t lick blue-green algae from their coats.

There’s more information at https://dnr.wisconsin.gov/topic/lakes/bluegreenalgae and https://www.dhs.wisconsin.gov/water/bg-algae/index.htm. You can also view a 2021 Wisconsin Water Week DNR presentation on blue-green algae here.Beaver Dam Lake is a nutrient-rich, very shallow impoundment so it’s highly susceptible to blooms. There are local and regional efforts to address the nutrient pollution which is fueling the blooms, but unfortunately the lake is in a similar situation to other shallow-nutrient rich impoundments throughout Wisconsin, in that the creation of these water bodies also inadvertently created conditions that foster blue-green algal growth.