It's that time of year again, when Iowa beaches heat up to the point that blooming algae becomes a real concern for swimmers. Last year was a record-setting summer for reports of this dangerous pollutant in Iowa lakes. Since 2006, the Iowa DNR has conducted testing in the public swimming areas it oversees. You can find their reports, here.

Blue-green algae is a common occurrence in Iowa during the late summer, when hot temperatures combine with pollution to create levels of harmful bacteria that can make people and pets who are exposed to it very ill.

Here's what you need to know about toxic blooming algae in Iowa:

Iowa State Park Beach Swimming Advisories

Our state park beaches are monitored weekly by the Iowa Department of Natural Resources (DNR) for microcystin. This toxin, produced by some types of blue-green algae, is the result of high levels of pollution combined with hot temperatures. It's common in the late summer months. When microcystin levels exceed 20 micrograms (ug) per liter, warning signs are placed near beaches to warn visitors that the water may not be safe for swimming. This table, created by the Iowa Environmental Council, shows test results dating back to 2006.

Toxic microcystin bacteria are dangerous to people, but also may kill fish and other wildlife when algae blooms are present.

Microcystin toxins float on top of water. They resemble paint and are bright green and/or blue. They also may look like pea soup.

Boating isn't necessarily safe in water where toxic algae flourishes.

Between Memorial Day and Labor Day of 2016, the DNR reported 37 places where microcystin levels were high enough to create unsafe swimming conditions. That was three more than the previous year, and a record for all years that the DNR has conducted testing for this pollutant.

It contaminated water is inhaled, it has been known to cause a sore throat, chest pain, allergic reactions, runny nose and eyes, and asthma-like symptoms.

Contaminated water poses a more serious threat to children and pets, as they are more likely to inhale water while playing.

In Iowa, the DNR has issued a total of 185 microcystin beach warnings since 2006. Two-thirds of those warnings have been in the last four years. Last summer, Des Moines Water Works found microcystin in already-treated drinking water.

This harmful bacteria feeds off of phosphorus and nitrogen that seep into our waterways from livestock waste and agricultural fertilizers. Although some effort is being made to engage in "nutrient reduction" plans that would protect important waterways from this dangerous pollutant, very little progress has been made on the issue.

The Iowa Nutrient Reduction Strategy estimates that only 8% of the nitrate in Iowa water comes from sewer runoff, and 92% is a result of agricultural pollutants. Recently, Des Moines Water Works sued the Board of Supervisors in charge of ten drainage districts over high nutrient levels in the drinking water. That lawsuit was dismissed by the United States District Court for the Northern District of Iowa on March 17. Des Moines Water Works serves 500,000 Iowa residents.

Green Valley State Park, located in south western Iowa, has frequent problems with toxic algae blooms during the hottest Iowa summers.

The Microcystin levels exceeded 20 ug/L according to testing conducted by the Iowa Environment Organization 34 times since 2006. Last summer, the water was unsafe for swimming seven times.

Black Hawk State Park is in western Iowa, just south of Storm Lake.

There were two times last summer when Denison Beach was unsafe for swimming due to toxic algae blooms. There was just one incident in 2015, but the beach was closed seven times in 2014.

Pine Lake State Park is located along highway 20 west of Waterloo in north central Iowa.

There are two lakes here and the park provides access to the Iowa River. The beach here was closed six times last summer due to toxic algae blooms, and three times in 2015.

Lake Keomah State Park is in south eastern Iowa near Oskaloosa.

The park doesn't have much of a history of problems with toxic algae blooms until last summer, when the beach was closed 4 times.

Viking Lake State Park is in western Iowa near the town of Red Oak.

This 137-acre lake has a 4.5-mile shoreline and a sandy beach on the west shore. This is a "no wake" area popular with fishermen. This lake doesn't have much of history of dangerous algae blooms before last summer, when the beach was closed four times.

Toxic algae blooms are a huge concern in Iowa during the late summer. Remember, not every beach is tested, so use your best judgement when you see floating green and/or blue algae in water where you, your children, and your pets may swim.