If there is a positive test result for bacterial contamination Greys and Rocky Nook beaches will have signs posted notifying it is unsafe to swim; if the testing is a presumptive false positive no swimming posting will still occur until confirmation test clears the waters. A false positive may occur if the test is too close to a hard rain with run-off or during a storm.
Guidelines for Cyanobacteria at Recreational Freshwater Locations
Cyanobacteria (sometimes called blue-green algae) occur naturally in freshwater, but under certain conditions they can multiply quickly, creating a highly concentrated area known as an “algae bloom”. Algae blooms can be harmful to humans and animals. Some harmful cyanobacteria produce toxins (known as cyanotoxins) that are dangerous at very low levels in surface waterbodies. These harmful algae blooms (HABs) may occur at any time in Massachusetts, but are most common in late summer and early fall.