Visitors to St. Joseph's Corby Pond are being told to avoid fishing and to stay out of the water.
A post on the city's Facebook page says a harmful algal bloom has been detected.
Some types of the blue-green algae can produce toxins that may affect the health of people and animals.
Signage to warn visitors will remain in place until 14 days after the bloom has completely disappeared.
The city also announced its contracted pond management company has treated the ponds for algae at Corby Pond and the Krug Park lagoon.
Statement from the city of St. Joseph's Facebook page:
People and animals are being asked to stay out of the water and avoid fishing at Corby Pond following the detection of a harmful algal bloom.
Signage is being placed at the pond to warn visitors and will remain in place until 14 days after the bloom has completely disappeared. The additional 14-day period is a precaution in case toxins were produced during the bloom.
Cyanobacteria, often referred to as blue-green algae, are responsible for harmful algal blooms. Some types can produce toxins that may affect the health of people and animals, the Missouri Department of Natural Resources says. However, the presence of a bloom alone does not indicate that toxins are present.
Although these blooms occur naturally, excess nutrients in a pond can cause them to develop more frequently or become more severe, according to the Missouri Department of Natural Resources. Nutrients can build up over time through atmospheric deposition, decomposition and runoff from the surrounding watershed during rainfall.
Eventually, these blooms generally disappear on their own. However, the City of St. Joseph had its contracted pond management company treat both Corby Pond and the Krug Park lagoon for algae on Tuesday.
A few dead fish have been observed in Corby Pond. According to Missouri Department of Natural Resources officials, the fish deaths are likely the result of low dissolved oxygen in the water rather than cyanotoxins, if toxins are present.
Visitors are asked to follow the posted warnings and keep themselves, children and pets out of the water until the warning signs have been removed.
