Environmental Public Health Tracking provides data and information on health outcomes, the environment, population, and exposures, including hazardous algal blooms occurring in water bodies of the USA, both freshwater and marine.

CDC Public Notice on Hazardous Algae Blooms
It is not possible to know if a large growth, or bloom, of algae or cyanobacteria (also called blue-green algae) is harmful just by looking at it. Some blooms make toxins (poisons), which can still be in the water even when you can’t see a bloom. Learn how to protect yourself and your loved ones from harmful algae and cyanobacteria, what to do if you or a pet is exposed to them, and how to help prevent these blooms.

Swimming and Wading.  Stay out of water with a bloom, rinse off if you or your pets are in contact with water
If you see signs of a bloom, stay out of the water and keep your pets out of the water. Do not fish, swim, boat, or play water sports in areas where this is possible harmful algae or cyanobacteria.
Do not go into or play in water that.

• Smells bad
• Looks discolored
• Has foam, scum, algal mats, or paint-like streaks on the surface
• Has dead fish or other animals washed up on its shore or beach

• Get in the water
• Drink the water
• Lick or eat mats of cyanobacteria or algae
• Eat or graze near the water
• Eat dead fish or other animals on the shore
• Go on the beach or shoreline

Drinking Water.
Follow local guidance about toxins in tap water If you are notified of cyanobacteria or their toxins in your public drinking water supply, follow guidance from your local or state government or water utility to reduce the chances of you or your animals getting sick.
Harmful cyanobacteria may grow in water bodies that supply tap water. Although many water treatment plants can remove these toxins, tap water can be contaminated in certain situations. Cyanobacteria can also produce substances that are not harmful, but can change the taste or smell of tap water.
If you have concerns about the appearance, smell, or taste of tap water that you are using, contact your water utility or health department. Consider using bottled water for drinking and cooking until the problem is resolved.
Don’t boil water contaminated with toxins. Boiling water does not remove toxins and can concentrate the toxin.

 
Fish and shellfish.
Be aware of advisories and health risks related to eating contaminated fish and shellfish
Avoid eating very large reef fish (such as grouper or amberjack), especially the head, gut, liver, or roe (eggs). Large reef fish may be contaminated with ciguatoxin, the algal toxin that causes ciguatera fish poisoning. See the U.S. Food and Drug Administration’s (FDA) Fish and Fishery Products Hazards and Controls Guidance for more information on reef fish associated with unsafe levels of toxins.
Check for and follow local shellfish and fish advisories before eating any fish or shellfish you collect yourself. Algal and cyanobacterial toxins in fish or shellfish have no taste or odor. Cooking or preserving food does not remove toxins. Thus, you cannot tell if the seafood is safe by just looking at, smelling, or tasting it.

• Check to see if shellfish beds are closed. State shellfish control authorities (usually state health departments or other state agencies) are required to control for toxins where harmful algal blooms are likely to occur and toxins could build up in shellfish. Common ways state authorities control for algal toxins include routine monitoring for toxic algae or shellfish and testing shellfish for toxins before or after harvesting. If levels of toxins are unsafe, state authorities will close the area for shellfish harvesting until shellfish are safe to eat.
• Check safety advisories from the Environmental Protection Agency’s (EPA) Fish and Shellfish Advisories and Safe Eating Guidelines website.