Boaters and swimmers in Padanaram Harbor might notice discoloration in the water after an abundance of algae, or “rusty tide,” appeared in waters south of the causeway.

According to Dartmouth Harbormaster Steve Melo, the cochlodinium algae bloom, which can be seen as large areas of water with a red to brown color, first appeared in Pananaram Harbor on August 8. The algae has been spotted throughout Buzzards Bay as well. Melo and officials from the state Division of Marine Fisheries took water samples on August 9, which confirmed the presence of the algae.

He said the current algae levels pose no threat to swimmers or shellfish, but could create problems for other fish in the harbor.

“The main problem is the algae deprives oxygen from the water, it uses that oxygen to grow,” Melo said. “We could end up with a fish kill.”

Melo said oxygen levels in the water could become worse if a fish kill occurs. When large groups of fish die at the same time, the decomposition can remove even more oxygen from the water.

There are two main causes that encourage the algae to grow: nitrogen pollution and exceedingly warm water temperatures, according to Melo. Nitrogen can enter the water from septic systems, wastewater treatment plants, fertilizers and other sources. The water temperature has been measured at more than 80 degrees recently as a result of a hot and humid summer. Melo added that he has seen occurrences of rusty tide in past years during hot summers.

For now, there is not much the Harbormaster’s Office can do except wait for the algae to clear out. Melo said the algae should begin to dissipate once the water temperature goes down, something he hopes could be helped by the weather.

“We’re hoping that the rain will cool off the surface temperature, which might drive the algae away,” Melo said.

Until then, the Harbormaster’s Office will continue to monitor the algae levels in the water and alert the public if there are any changes.