Harmful Algae Blooms: How Boaters Spot Them, Check Advisories and Clean Up Afterward

The CDC's first prevention step is to check swimming, fishing and shellfish advisories before you go. Where to look:

• Your state's HAB page. Most states post them through the health department or the environmental agency (search "[your state] harmful algal bloom advisory"). Oregon and New York, for example, keep lists of current blooms, and Oregon offers email and text alerts.
• Forecasts for big waters. NOAA publishes a Lake Erie HAB forecast with satellite images of where the bloom is during the season.
• Signs at the ramp or beach.

No advisory doesn't mean safe. The CDC notes agencies can't monitor every lake, and Oregon says most of its waterbodies aren't monitored at all.

At the ramp and on the water, look for what the CDC and state agencies describe:

• Spilled-paint look, scum, foam, or floating mats or globs
• Water color that's pea-green, blue-green, brown, yellow, orange, red or even white
• A bad smell like rotten eggs or rotting plants as the bloom decays
• Dead fish or animals on the shore
• Mats on rocks or the bottom in clear water (benthic blooms); bits can break off, float, and dry along the shoreline, still toxic

Oregon notes scums are often thickest early in the day and can be pushed by wind into one corner of a lake. The bloom you saw at 8 a.m. in the cove may be across the lake by afternoon.

If the ramp area is scummy or an advisory is posted:

• The simplest choice is another lake or another ramp upwind of the bloom.
• If you go out, stay out of the water: no swimming, wading, skiing, tubing or wakeboarding in or near the bloom (CDC, Oregon).
• Run at idle speed through any discolored water so you don't throw spray into the boat, and keep people seated away from the spray.
• Don't anchor or raft up in a scummy cove.

On the coast: red tide. In Florida and Texas, red tide is caused by the microscopic alga Karenia brevis. NOAA's National Centers for Coastal Ocean Science (NCCOS) says these blooms can cause breathing irritation and eye irritation in people, kill marine life and lead to shellfish closures. The irritation comes through the air, so you can feel it on the boat even if nobody touches the water. NCCOS publishes a regular red tide forecast for Florida and Texas and says the risk of respiratory irritation is highest when the wind blows onshore or along the shore. Blooms are patchy and change through the day. If people aboard start coughing, sneezing or getting itchy eyes, move the boat away from the discolored water and upwind of it; anyone with asthma or other lung problems should keep clear of red tide areas altogether and go ashore if symptoms don't ease.

This is the biggest risk on board. The CDC's advice for pets: don't let them drink the water, swim or play in it, eat near it, eat algae, or eat dead fish on the shore, and don't let them lick their fur if they do get wet. Bring a water bowl and fresh water so a thirsty dog isn't tempted by the lake. Our pet guide covers life jackets and boarding.

The CDC says to wash the animal off immediately with clean water so it can't lick cyanobacteria off its fur. Wear gloves, use tap water from your boat's freshwater tank or bottles, and towel the dog dry. Then call a vet right away if you see any of these within a day or so (CDC list): low energy, not eating, vomiting, stumbling or falling, foaming at the mouth, diarrhea, drooling, tremors or seizures. Don't wait to see if it gets better; there's no antidote and death can come within hours. The ASPCA Animal Poison Control Center (1-888-426-4435) and the Pet Poison Helpline (1-855-764-7661) can help; both charge a fee.

• Rinse off right away with tap water (sink, shower, hose); the CDC recommends this after any contact with possibly bloomed water. Use soap if you have it (Oregon).
• Watch for the symptoms New York lists: diarrhea, nausea or vomiting; skin, eye or throat irritation; allergic reactions or breathing trouble.
• Call Poison Control (1-800-222-1222) with questions, and see a doctor if symptoms appear. Say the person was in a bloom.

Algae mats and scum can load up a raw-water strainer just like weeds do. After running through a heavy bloom:

• Watch your temperature gauge and outboard telltale; a weak stream can mean a clogged intake.
• With the engine off and the seacock closed (inboard/sterndrive), check and clean the raw-water strainer as in our strainer guide. Wear gloves.
• Don't fill the livewell or washdown from bloom water, and don't run a watermaker in a bloom (New York says never to drink or make ice with untreated surface water; Oregon says personal filters can't remove the toxins).
• Never top up your freshwater tank from a lake hose or spigot that draws untreated lake water.

There's no special federal decontamination procedure for boats that have been in a bloom. Health agencies tell you to rinse with clean water after contact (CDC, New York), so fold it into the clean-drain-dry routine you already do for invasive species:

• Pull the drain plug and drain bilge, livewells and ballast at the ramp's drain area, not into a storm drain.
• Rinse the hull, trailer bunks, rollers and lights with tap water, and scrub off any green film near the waterline with boat soap and a soft brush.
• Rinse ropes, fenders, anchor, tubes, life jackets and fishing gear, and let them dry in the sun.
• Wear gloves, and keep kids and dogs away from the dirty runoff.

Our clean-drain-dry and hull-cleaning guides cover the details, and the inspection-station guide explains what to expect if a state checkpoint stops you.

Flush the engine with fresh water after a day in bloom water, the same way you would after salt water. Outboards run only on external flush muffs or in a test tank; a built-in flush port is used with the engine off unless your owner's manual says otherwise. Inboards and sterndrives never run dry. See our freshwater flush guide.

• Follow the advisory. The CDC says to check and follow local fish and shellfish advisories, and that toxins have no taste or smell and survive cooking.
• Oregon's position: the risks aren't fully known, so it recommends not eating fish or shellfish from an area with an active bloom. If you do, the safer choice is to remove all fat, skin and organs before cooking and rinse fillets with clean water.
• New York's health department says simply: don't eat fish caught from areas with blooms, and don't swim, fish, boat or wade in them.
• Shellfish in salt water: states close harvest areas when testing shows they're unsafe. Never harvest from a closed area.

Clean fish at home or a fish-cleaning station with tap water, not in the lake.

The CDC asks you to report blooms and illnesses to your health department, and most state HAB pages have an online report form (Oregon has separate forms for human and animal illness). A photo and the GPS position from your chartplotter help agencies decide where to sample.