Health departments in Vilas and Oneida counties have begun monitoring public beaches for the 2026 summer season in efforts to keep swimmers and pets safe from bacteria such as E. coli and blue-green algae.

According to health officials at Oneida County Health Department (OCHD), E. coli infection symptoms can be mild or severe and include diarrhea, abdominal cramps, fever, or nausea and vomiting.

“If you have been in the water and think you have an E. coli infection, contact your local health department and seek medical attention, if symptoms are severe,” OCHD said.
Vilas County Public Health Department (VCPHD) conducts beach monitoring at several locations from Memorial Day weekend through Labor Day weekend each year. The department said beaches are checked for fecal coliforms and Escherichia coli (E. coli). These bacteria show that there may be more hazardous bacteria in the water.

Beaches being monitored in Vilas County include Crystal Lake in Boulder Junction, Big Arbor Vitae and Brandy lakes in Arbor Vitae, Black Oak Lake in Land O’ Lakes, Hunter and Torch lakes in Conover, Eagle and Silver lakes in Eagle River, Koller Memorial Park in Manitowish Waters, and Little Star Beach in Star Lake.

Based on beach water sample results, a beach is marked as “open for swimming,” posted with an “advisory” or posted as “closed.”

VCPHD said if an advisory or closure is posted, the beach is resampled that day, and sampling will continue until bacteria levels are at a safe level for swimming.

“E. coli contamination of the water can come from a number of sources, such as waterfowl, dirty diapers, dogs, and rainwater runoff,” the department said.

In Oneida County, beaches set for monitoring include Maple Lake Beach in Three Lakes, Sugar Camp Public Beach in Sugar Camp, Torpy Park in Minocqua, and Buck Lake and Boom Lake beaches in Rhinelander.

Lake users can help prevent E. coli outbreaks in swimming areas by picking up dirty diapers and fecal matter from dogs, not feeding seagulls and other birds, and keeping watch for birds flying over water recreation areas.

They also should check water conditions and be aware that E. coli levels can be higher after heavy rain because dirty water can wash into lakes and beaches. “If you see algal blooms, avoid the water,” OCHD said.

Users also should look for the signs at the beach; OCHD staff will have yellow advisory signs and red closure signs posted at the beach if E. coli levels are high.

The most recent round of testing by OCHD found that all tested beaches in Oneida County were safe for swimming.

Blue-green algae

Health department staff will also monitor the beaches for cleanliness and for blue-green algae blooms. Lake users are reminded that conditions can change quickly, so swimmers should be on the lookout if the water looks like pea soup, green or blue spilled paint, or has a green scum layer on the surface.

VCPHD explained that algae and cyanobacteria (also called blue-green algae) are plant-like organisms that live in water.

True algae are a vital part of lake systems; however, blue-green algae are not true algae. It is a photosynthetic bacteria known as cyanobacteria, which can cause illness and death in humans and animals.

Algae blooms are caused by a sudden increase in algae cells in certain areas of water. Little wind, warm water, sunlight, and plentiful nutrients — especially phosphorus — all increase the chance that a bloom will occur. Warm weather and heavy rain that wash agricultural and residential fertilizers (which contain phosphorus) into the water can start a bloom.

In Wisconsin, blooms typically occur during the warm-weather months between mid-June and mid-September.

According to VCPHD, blue-green algae float to the surface, where they can form thick scum layers or mats. The surface may look bubbly or frothy. It is impossible to tell if an algal bloom is blue-green algae from simply looking at it, and is best to treat every bloom as if it could be dangerous.

“If you come across an area where you believe blue-green algae may be present, do not swim, wade, or boat through the blooms,” VCPHD said. “Make sure not to let your pets drink or swim in any water where algal blooms may be present. If you or your pet comes into contact with blue-green algae, wash your body with soap and clean water as soon as possible. If ingested, call your primary care provider or veterinarian as soon as possible.”

For more information about Vilas’ sampling process or procedure, contact the VCHPD at 715-479-3656 or visit vilascountywi.gov for more information.

For the latest staff updates from OCHD, visit publichealth.oneidacountywi.gov or follow the department on Facebook. OCHD also can be reached by calling 715-369-6111 or emailing eh@oneidacountywi.gov.

To report a blue-green algae bloom or illness from lakes, contact the county health department.