March 19, 2025

‘Pink Ice’

Algae bloom gives Roorda Refuge ice rare hue

By Mike Mendenhall

Pockets of pink algae, like the one pictured, can be see throughout the ice covering the pond at Roorda Wildlife Refuge southwest of Monroe. According to Jasper County Conservation, an algae bloom this size is rare during winter months, and the micro bacteria has given the ice a pink hue. (Mike Mendenhall)

Anglers hitting the ice at Roorda Wildlife Refuge in the last few weeks might have noticed something a little peculiar just below the surface. The ice has turned a subtle shade of pink.

A pink algae bloom has developed below the ice of the wildlife refuge’s pond off Highway 163 southwest of Monroe. In some areas where the algae has risen closer to the surface, it has created little concentrated, plumb colored pockets of the micro bacteria in the ice.

According to Jasper County Conservation, an algae bloom this large is rare this time of year and has peaked the interested of the area’s scientific community.

Jasper County Conservation Director Keri Van Zante said it takes a specific set of conditions in the water for an algae bloom of this size to form during the winter.

She briefed the Jasper County Board of Supervisors on the algae bloom at its regular Jan. 30 meeting. She said the micro bacteria, which make up the pink algae, can produce a cytotoxin. But according to the conservation director, this bloom is not dangerous. So ice fishermen/women and outdoor enthusiasts can enjoy the extra color of the unique “pink ice.”

However, Van Zante said if ice anglers come in contact with the algae, they should take mild precautions.

“(Toxin) is not likely in this situation as the pond is very deep and has a continuous stream of fresh water flowing into it,” Van Zante said. “Fish won’t accumulate any such toxins in their tissues, so they are safe to cook and eat. To be safe, my advice would be that people should wash hands after contact with the water, and probably shouldn’t eat the pink ice.”

According to Grace Wilkinson, associate professor at Iowa State University’s department of ecology, evolution and organismal biology, the algae is referred to as a cyanobacterial Planktothrix in the scientific community. It is well adapted to low light, cold environmental conditions and is common in Iowa.

Van Zante said the Iowa Department of Natural Resources was scheduled to collect samples of the algae last week to confirm it is Planktothrix. The pond is about 30 feet deep, and Van Zante said the algae likely lays at lower depth where the water is coldest during the summer months and during the winter, rises to the top.

Contact News Editor Mike Mendenhall at mmendenhall@newtondailynews.com