Courier Life’s
July 12, 2012 / News / Park Slope / Meadows of Shame

Azolla caroliniana in Prospect Park

Prospect Park slime is no good for fish, birds, turtles, park advocates say

Brooklyn Daily
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An invasive pond fern has taken over the Prospect Park lake, and nature lovers fear the verdant gunk will choke out aquatic life and make turtles blind.

A rapidly growing species called azolla caroliniana has formed a sprawling green and red sheen on the surface of the lake by the boathouse in the past few weeks — potentially hogging oxygen and blocking sunlight, according to Cornell University’s Chuck O’Neill.

“It has a tendency to crowd out other plants and cause mortality in fish,” said O’Neill, who specializes in the study of invasive species. “It’s a nuisance.”

The researcher says contaminated fishing or boating equipment could have also triggered the bloom, which first made waves last year but returned this summer in greater volume.

That worries park watchdogs, who have long claimed the gunk scares away waterfowl, blinds turtles, and sickens mammals.

“It’s a serious problem; it can kill aquatic wildlife in the watercourse,” said park advocate Ed Bahlman.

A warm spring season likely triggered excessive amounts of the fern, which has spread rapidly in the past three months and is “relatively new” to Prospect Park altogether, according to taxonomists with the Brooklyn Botanic Garden and the New York Botanical Garden who tested the water after the stuff coated the lake last fall and determined it was “azolla bloom.”

Dubbed water velvet and mosquito plant, the new strand aquatic life is the “Jekyll & Hyde” of water weeds — serving as a crop-boosting miracle plant as well as an oxygen-sucking ecosystem invader, according to some experts.

The fern, which is considered “the best adapted of all species for subsistence on mud,” can help balance nitrogen levels in waterways. And when it’s combined with other strands of algae, it can make plants and crops more fertile, researchers say.

A Prospect Park Alliance spokesman, Paul Nelson, sent this paper a link to the agency’s website stating that the green and red gunk is not toxic and that scientists will continue to monitor it.

“We expect and hope that, being a native species, [it] will not have harmful consequences for our ecosystem,” the website notes. “That being said, we are watching closely.”

Authorities in Great Britain and China have worked to eradicate the same strand of water weed, saying it kills native wildlife and floods waterways.

Reach reporter Natalie O'Neill at or by calling her at (718) 260-4505.

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