What's growing on Tilden Park's Lake Anza?

What’s that stuff growing on Tilden Park’s Lake Anza?

What's growing on Tilden Park's Lake Anza?
Tilden Park’s Lake Anza is completely covered with a thick layer of moss-like vegetation called Azolla. (Photos by Pete Cruz)
Close-up of the growth that covers the lake.

SAN FRANCISCO EAST BAY, CA (May 1, 2022) — If you happen to pass by Lake Anza at Tilden Regional Park near Berkeley, you can’t miss the mat of yellow-bronze vegetation that is blanketing almost the entire lake surface.

The plant is called Azolla, common name mosquito fern. According to the park district staff, it is native to California and not toxic, but usually occurs in smaller, seasonal patches. The mild winter weather has enabled it to spread across the whole 10-acre lake.

Although the plant is a nuisance, district staff says it does have the beneficial effect of using up excess nutrients that harmful blue-green algae need to bloom. The fern also keeps water temperatures cooler for the native species of trout that live in Lake Anza.

The district will continue to monitor the lake to see if the Azolla dies off during the hot summer months. The growth can be removed if necessary.

And since 2020, the district has been sustaining the water quality of the lake for fish by pumping oxygen into it through a hypolimnetic oxygenation system (HOS).

No swimming

Unfortunately there won’t be any swimming in Lake Anza this season, but not because of the Azolla. The swim beach will be closed for various scheduled maintenance projects, and due to ongoing water quality uncertainty.

Much of the Lake Anza parking lot is fenced off now, because a path is being constructed there for wheelchair users.

Swimming is also off the agenda this summer at Shadow Cliffs in Pleasanton, because the drought has made the lake’s water level so low that the swim beach is high and dry.

Working on the railroad

As always, a busy weekend is on the calendar at Ardenwood Historic Farm in Fremont.

First on the agenda is a train track construction demonstration from 10 a.m. to noon and 1 to 3 p.m. on Saturday, May 7. Crews will be working on the railroad all the livelong day at the Ardenwood train station, and will talk about tools and techniques at 10:30 a.m. and 1 p.m.

Budding artists of all ages will enjoy a corn mosaic craft session from 11 a.m. to noon on the same day. All ages will enjoy using multi-colored, freshly harvested kernels to create a work of art.

Then from 1:30 to 2:30 p.m. that afternoon, you can try your hand at stilt walking. Back in the day, stilts were not just a toy. Farmers used them for several work purposes.

And of course Sunday, May 8 is Mother’s Day. Ardenwood will celebrate it from 11 a.m. to 3 p.m. with live music. You can play a game of croquet or bocce ball, and create a floral crown for Mom. There’s also an elegant buffet brunch, for which advance reservations are required. Or you can purchase food from the café.

For brunch information, go to www.ardenwoodevents.com/mother-day. The corn mosaic and stilt programs are drop-in, registration is not required.

Ardenwood is located at 34600 Ardenwood Boulevard, just north of Highway 84. For information on admission fees and programs, call 510-544-2797. Parking is free.

Marsh hike

Nearby at Coyote Hills Regional Park there’s a walk through the marsh from 10 to 11:30 a.m. on Sunday, May 8, led by naturalist Maeron Yeshiwas. The group will check out the plants and animals that live in the marshland, then use scientific tools to investigate further.

All ages are welcome, but parent participation is required. It’s a free, drop-in program; registration is not necessary. Meet at the visitor center.

Coyote Hills is at the end of Patterson Ranch Road off Paseo Padre Parkway in Fremont. There’s a parking fee of $5 per vehicle. For information, call 510-544-3220.

Colorful walk

Naturalist Claudia Muñoz will lead another of her series, “People of Color: Evening Walks & Talks” from 6 to 8 p.m. on Wednesday, May 11 at Wildcat Canyon Regional Park in Richmond.

This is a challenging, 2½-mile climb to some beautiful views, during which Claudia will talk about the local plants and animals. The program is bi-lingual in English and Spanish.

Registration is not necessary and the program is free. Meet at the park’s Alvarado Staging Area, which is on Park Avenue off McBryde Avenue in Richmond. For information, call 510-544-3176.

There are lots of other great activities planned in the regional parks in coming days. Check out the website, www.ebparks.org.

Ned MacKay writes a regular column about East Bay Regional Park District sites and activities. Email him at nedmackay@comcast.net.