The Lake Pontchartrain Basin Foundation is warning about the presence of "harmful algal blooms" near the north shore of Lake Pontchartrain from the Tangipahoa River to Slidell.
Lake-goers and boaters are advised to keep themselves and their pets away from the blooms.
The algal blooms are green or blue-green, have a scummy or viscous consistency, and usually smell bad.
It is generally unsafe to swim in water with algal blooms, and even boaters may be exposed to the toxins of the blooms through water spray.
The toxins in the bloom can lead to serious health effects such as rashes, stomach or liver illness, respiratory problems and neurological effects.
The algal blooms can also have a negative impact on the marine ecosystem, causing fish kills, and causing "dead zones," or oxygen depleted areas that can cause a severe impact to oysters and other bottom species of fish.
The Pontchartrain Basin Foundation warned that the opening of the Bonnet Carre Spillway might cause algal blooms in Lake Pontchartrain as the freshwater from the Mississippi River delivered a high concentration of nutrients to the lake.
Algae are naturally present, but harmful blooms form during conditions that include high nutrient concentrations, warm temperatures, ample sunlight, and slow moving winds.
"With weather conditions due to remain the same, that's to say warm temperature and low winds, we can expect this bloom to increase in size and intensify for at least a week," Dr. John Lopez said. "Depending on weather conditions, we still expect the lake to return to normal conditions in the next two to three months."