Boulder County warns residents to keep an eye open for summer algal blooms

As summer temperatures swing into the 90s, you and your four-legged friends are likely looking for ways to stay cool. And though a dip in one of our local ponds may look tempting, be aware that standing bodies of water may be home to blue-green algae.

You may have seen the caution signs at trailheads this summer or in summers past, typically at Coot Lake, the Boulder Reservoir, or, most recently, at Wonderland Lake: "Caution: Harmful Algae May Be Present."

Historically in Colorado, blue-green algae blooms have mainly posed a problem for dogs, although the algae is also toxic to humans if ingested. But what is blue-green algae and how can you tell if it is present in a standing body of water?

Blue-green algae isn't actually algae at all, but rather cyanobacteria, a type of bacteria that are capable of photosynthesis. Cyanobacteria are native to Colorado waters and are a healthy part of an aquatic ecosystem, helping support fish and other aquatic life. But too much nitrogen or phosphorus in the water can cause blue-green algae to form blooms and scums. Most common during hot, sunny weather, these blooms are usually found in standing or slow-moving bodies of water and produce toxins that can cause illness in humans, pets, and other animals that come in contact with the algae.

Although cyanobacteria are native, according to Boulder County, warmer temperatures, stagnant water, and nitrogen and phosphorus (nutrient) loading from fertilized lawns and other sources can facilitate unhealthy algae and cyanobacteria growth. Known as harmful algae blooms (or HABs), these cyanobacteria blooms are similar to another cyanobacterium bloom that happens in marine or saltwater-the Red Tide.

In the last week, cases of harmful blue-green algal blooms were reported in North Dakota, Nebraska, Florida, California, and Texas. This problem is not unique to Colorado, but rather a problem unique to any standing body of water that could become a petri dish for cyanobacteria blooms in the warmer summer months.

Boulder County notes that it does not test local bodies of water for current levels of blue-green algae as the levels can change hourly. It's tricky-a here one moment, gone the next kind of transient algal superbloom.

So what can you do to avoid potentially toxic HABs? First, keep an eye out for signs of blue-green algae blooms. According to the Colorado Department of Public Health and Environment, cyanobacteria blooms may look like thick pea soup or spilled bluish-green paint on the water's surface. They can also create a thick mat of foam along the shoreline.

Other precautions you can take are to keep your dogs on leash to keep them out of the water or from finding algae that may have washed up on shore. People should also avoid wading or swimming in any ponds or lakes where suspected algal blooms are present.

Anglers should use caution and follow state recommendations for thoroughly cleaning any caught fish and discarding the guts accordingly. Boating or fishing may be entirely prohibited in some cases, and you should check with local land management agencies for the most current cautions and restrictions.

Not all algae are harmful, but if you are uncertain, it is best to avoid the water. With the proper precautions and an awareness of what to look for, you can keep yourself, your family, and your pets safe this summer.