City Warns Residents to Avoid Corby Pond After Harmful Algal Bloom Found

ST. JOSEPH, Mo. — The City of St. Joseph is warning residents to stay out of the water, keep animals away and avoid fishing at Corby Pond after a harmful algal bloom was discovered.

The city said warning signs will be placed around the pond and will remain in place until 14 days after the bloom has completely disappeared.

The additional two-week period is being used as a precaution in case toxins were produced during the bloom.

What is a harmful algal bloom?

Despite commonly being called “blue-green algae,” the organisms involved in many freshwater harmful algal blooms are actually cyanobacteria, a type of bacteria that uses sunlight to produce its own food.

Cyanobacteria naturally occur in water and are part of aquatic ecosystems. Problems can develop when conditions allow the organisms to multiply rapidly and become concentrated in the water, creating what is known as a bloom.

Not every algal bloom is dangerous. However, some cyanobacteria can produce chemicals known as cyanotoxins, which can make people, pets and livestock sick. Missouri environmental officials say it is not possible to determine whether a bloom is producing dangerous toxins simply by looking at the water.

Blooms can take on several different appearances. The water may become bright green or blue-green, but blooms can also appear white, reddish or yellowish-brown. In some cases, the water can resemble pea soup, while other blooms create streaks or patches that look like paint spilled across the surface.

Thick foam or scum can also accumulate along the shoreline or on the surface of the water. As cyanobacteria die and decompose, they can produce an odor similar to rotting plants.

The appearance of a bloom can also change quickly. Wind, rain, currents and other movement in the water can cause cyanobacteria to shift locations or concentrate in different areas of a pond or lake.

Why can the blooms be dangerous?

People can potentially be exposed to cyanobacterial toxins by swallowing affected water or coming into direct contact with it. Missouri DNR says exposure can cause symptoms ranging from skin irritation and rashes to vomiting, diarrhea, dizziness and other illnesses, depending on the toxin and level of exposure.

Animals can be particularly vulnerable because they may drink contaminated water, swim through concentrated algae or lick algae from their fur afterward.

Missouri DNR says pets and livestock exposed to cyanobacterial toxins can experience symptoms including vomiting, diarrhea, weakness, difficulty breathing, seizures and, in severe cases, death.

Harmful blooms can also affect the pond itself. Large blooms can reduce oxygen levels in the water as organisms die and decompose, potentially leading to fish kills and other impacts on aquatic life.

What causes a bloom?

Algal blooms can occur naturally, but excessive nutrients in a body of water can allow them to develop more frequently or become more severe.

According to the city, nutrients can accumulate in a pond over time through atmospheric deposition, the decomposition of organic material and runoff entering the pond from the surrounding watershed during rainfall.

Lakes and ponds are among the water bodies most likely to experience cyanobacterial blooms, although they can also develop in slow-moving or pooled streams.

One reason officials remain cautious even after a bloom is no longer visible is that appearance alone does not establish whether toxins are present. The Environmental Protection Agency notes that cyanotoxins can remain in water before or after a visible bloom is observed.

For that reason, the City of St. Joseph is asking the public to avoid Corby Pond until the warning signs are removed.