Beach water sampling

We monitor 22 Dane County area beaches for E. coli bacteria and blue-green algae.

Our goal is to prevent harmful bacteria and toxins from making people sick while they enjoy our lakes and beaches.


Beaches We Monitor

Lake Mendota:
James Madison, Lake Mendota County Park, Maple Bluff, Marshall, Memorial Union, Spring Harbor, Tenney, Warner Park

Lake Monona:
BB Clarke, Bernies, Brittingham, Esther, Frost Woods, Hudson, Olbrich, Olin, Schluter

Lake Waubesa:
Goodland, McDaniel

Lake Wingra:
Vilas

Stewart Lake:
Stewart Lake

Verona:
Fireman's Park Beach


What we Test Water For

E. Coli Bacteria

  • Germs found in water are most commonly bacteria, viruses, or parasites from human or animal feces. These germs can cause swimmers to become sick.
  • Because testing for all the germs in the water that could make you sick is time-consuming and expensive, scientists and beach managers use indicator organisms for monitoring. For fresh waters, Escherichia coli (E. coli) is the best indicator to tell if there are germs in the water that can make people sick.

Blue-Green Algae (Cyanobacteria)

  • Blue-green algae (cyanobacteria) can form blooms in freshwater that can be toxic to people and animals, causing a variety of symptoms.
  • Conditions like high nutrient levels in the water, sunshine, and other factors can create blue-green algae blooms.

When We Collect Water Samples

E. coli Bacteria

  • We collect water for E. coli testing at least once a week at each beach.
  • If bacteria levels are high, we close the beach for swimming. We test again each weekday until the sample meets an acceptable bacteria level, then the beach is reopened for swimming.

Blue-Green Algae (Cyanobacteria)

  • We look for blue-green algae blooms at least once a week at each beach.
  • In addition, if a lifeguard or beach user reports an algae bloom, we will follow-up at that beach as soon as possible.
  • If a blue-green algae bloom is present, we will collect water daily (M-F) to test for blue-green algae toxins.
  • The beach will stay closed for swimming until levels of blue-green algae are acceptable.

Beach Closures for Swimming

  • A beach water quality closure means that the water has been found unsafe for swimming.
  • Beach water quality closures happen when levels of E. coli or blue-green algae toxins are higher than established safety limits.
    • For E. coli, this limit is 1,000 MPN/100 mL.
    • For blue-green algae, this limit is 8 ppb or higher of toxin-producing algae and/or microcystin toxin.
  • You can still enjoy the sandy area of the beach and other park facilities while avoiding contact with the water.

Conditions Can Change Quickly

Many factors can influence water quality:

  • Recent weather conditions like wind or rain
  • Time of day
  • Waterfowl and wildlife at the beach
  • Number of people at the beach
  • Physical characteristics of the beach.

It’s possible for conditions to vary significantly throughout the day and from day-to day.

Before swimming, always take an overall look at water conditions. Conditions can change quickly, and testing results may not always reflect real-time water quality.

A few things to remember:

  • You cannot always see or smell when water conditions are poor.
  • Swimming is not recommended after a heavy rainfall because bacteria levels in the water may be high.
  • People and pets should stay away from the water and avoid contact if a blue-green algae bloom is in the water (most often blue-green in color, but can also be reddish-purple, or brown), or the water is murky.
  • Do not drink lake or river water.
  • Wash your hands before eating if you have been in the water.
  • Wash your pet after swimming.
  • Stay out of the water if signs tell you it is not safe for swimming.
  • Call us at (608) 266-4821 if you think you see a blue-green algae bloom.

How we communicate about beach water quality


Request Testing for Your Water Event

If you are hosting an event where people will be in the water, consider additional testing for E.coli and blue-green algae. See our fact sheet for different options and costs. Contact us at 608-266-4821 to schedule services.