Many parkway visitors have noticed a dense fern covering much of the pond at Sailor Bar
this year. This floating fern is in the genus Azolla, often called mosquito ferns, and is believed to be native to California.
While non-toxic or otherwise dangerous, a dense population of Azolla can block light from the water and deplete water oxygen levels as they decompose.
“In California, the general consensus is that we have two species present – Azolla filiculoides, or ‘Common Mosquito Fern,’ and Azolla microphylla, also known as ‘Mexican Mosquito Fern,’” said Carl Rothfels, a biology professor with UC Berkeley. “This latter species is sometimes called Azolla mexicana -- it's not clear whether A.microphylla and A.mexicana are separate species.”
Both species of Azolla are thought to be native to California, although they have boom-and-bust population cycles that make them seem like they are invasive. It seems that this year the populations in the Sacramento area are unusually large.
The Department of Regional Parks
is currently working with Rothfels to determine why this fern is so abundant this year and what, if anything, we can do to curb its growth.