A Marin County Parks crew at Lagoon Park removed water primrose, an invasive aquatic plant, from the shoreline on Thursday afternoon.
Water primrose is the common name for several aquatic plants in the Ludwigia genus, and one invasive species, Uruguay water primrose (Ludwigia hexapetala), is known to grow in waterways in California.
The plant forms a thick, dense mat of aquatic vegetation on and below the water’s surface, impeding water movement and reducing habitat for native plants, fish and waterbirds.
Researchers with the U.S. Geological Survey have studied the plant’s expansion in marshes of the upper San Francisco Estuary. The plant is identified by long, narrow leaves and upright, sprawling stems, along with small yellow flowers.
While operating a backhoe to remove the plant, Marin County Parks Supervisor Donald Gallerani noticed that a Great Egret was following his bucket, waiting to catch fish lurking below the vegetation mats. Gallerani ultimately had to pause his work to allow the waterfowl to fish.
Marin County Parks describes Lagoon Park as a 10-acre park on the Marin County Civic Center campus. The lagoon is used by ducks, geese, shorebirds, fish and frogs. Fishing is allowed, but the county says the water is not maintained for people or pets and prohibits swimming and boating.
The county parks crew’s work on Thursday involved removing the invasive weed from the lagoon. Water primrose can grow from fragments, so aquatic plant material needs to be handled carefully to ensure that it doesn’t take root in another waterway.