Kayakers paddle past Pleasant Valley Beach at Moraine State Park in July 2022 in Muddy Creek Township. Butler Eagle file photo

According to the Butler County Tourism & Convention Bureau, more than two million visitors come to Moraine State Park each year. Many of them take a dip in the park’s central attraction, the massive man-made Lake Arthur, which measures 3,225 acres in area and has 42 miles of shoreline.

But humans and wildlife aren’t the only ones who love to go swimming in Lake Arthur. Around this time of year, an uninvited guest loves to make itself at home in the lake: algae.

Harmful algal blooms, or HABs, occur when toxin-producing cyanobacteria multiply due to excess nutrients in a body of water, typically in bodies of freshwater during the summer. These can lead to a depletion of oxygen within the water, as well as fish die-offs.

While they can vary in appearance, a good sign of an algae bloom is discolored, murky water that looks as if paint has been spilled on top of its surface. The blooms vary in color from blue-green to green and even red.

Indeed, on Thursday, July 4, Harmony resident Libby Miskevich posted a photograph on social media of what is purported to be algae bloom along Lake Arthur.

“Some small, localized blooms have been seen at different locations around the lake,” said Dustin Drew, park manager at both Moraine and McConnells Mill State Park. “There have been no impacts to the swimming areas at this time.”

Drew said algae blooms are not uncommon on Lake Arthur and Moraine monitors its swimming areas for them.

“It is very difficult to test the possible toxicity of a bloom in a timely manner, so we do monitor swimming areas, where there is the highest chance of contact with the water,” Drew said. “We would restrict swimming if it appeared a widespread bloom was present. We have signage posted around the park to educate visitors, and we also recommend dog owners avoid letting their dog in any water that looks like it may contain a bloom.”

By going into water with harmful algal blooms present, humans and animals run the risk of exposing themselves to harmful cyanotoxins, which can cause nausea, vomiting, diarrhea, stomach pain and other ailments.

Pennsylvania currently maintains a dashboard of harmful algal bloom water sampling data dating back to 2018. According to the dashboard, no harmful HAB activity has been detected at Moraine in the past year, or at any point in the 2020s.

However, the Pennsylvania Department of Health collected harmful algal bloom samples from Lake Arthur and Pleasant Valley Beach in July 2019. That year, cyanobacteria activity was measured at 49,600 natural units per milliliter at Lake Arthur.

For reference, the cyanobacteria density required to reach the “avoid contact” level is 1,500 natural units per milliliter.

This sample also contained 12.6 milligrams per liter of a cyanotoxin known as Microcystis. If enough is ingested, this toxin can cause gastrointestinal damage and liver failure, according to the National Institute of Environmental Health Sciences.

“If a person would come in contact with an algal bloom, it is recommended they wash off any skin that came in contact as a precaution,” Drew added.