California State Parks environmental scientist Dan Shaw recalls when the aquatic weeds along the shore of Emerald Bay were so tall the tops curled on the surface.
“There were people who worked here for years that wouldn’t swim here because it was too weedy,” Shaw said, as he stood on the dock near Vikingsholm Wednesday. “The weeds would wash up on the beach.”
Today, much of the iconic bay’s shoreline is sparkling clear and free of Eurasian milfoil, the aquatic invasive species that mucked up the area. Swimmers splashed around the roped-off area Wednesday. Kayakers came and went from the sandy beach near Parsons Rock.
The Tahoe Resource Conservation District, the Tahoe Regional Planning Agency and California State Parks credit the improvement to a decisively low-tech program that has been implemented below the water’s surface over the past three years.
“We treat the plants with bottom barriers that block the light to kills the plants as well as some diver-assisted suction removal,” said Jim Brockett, an aquatic invasive species control program coordinator with TRCD. “The barriers need to stay on top of the plants for eight weeks or so and it’s very effective at killing the plants.”
Since the program started in Emerald Bay, about six acres of severe milfoil infestations have been treated with the tarp-like barriers. In those areas, the lake bottom is sandy and easily visible.
“The infestations at Vikingsholm Pier and the swim beach are virtually eradicated,” Brockett said. “There are still a handful of plants there that come up each year, but it’s down to a maintenance level at both of those locations. “
Before the program started there were three main problem areas: one near Parsons Rock, one at the Vikingsholm swim beach and another farther south at Avalanche Beach. Divers Sean and Angie Murphy of Wet Leprechaun Dive Services, who are contracted for the job by the TRCD, spread the 10-foot-wide, 40-foot-long black barriers at the Avalanche Beach site Wednesday.
After dumping the barriers off the boat, divers systematically select a length of weedy area to cover. They then unroll the barrier, tucking it under and adjusting it over the logs and rocks on the bottom. When it’s stretched, they stake it in and leave them for eight weeks. When they lift the barriers, they collect the dead weeds.
“We’re not doing rocket science out here,” Shaw said. “We just need have to have the skills, the people and some resources.”
The most common invasive aquatic plants are curly leaf pondweed and Eurasian milfoil. Curly leaf pondweed is not present in Lake Tahoe. It’s unclear exactly when milfoil was spotted in the area, Brockett said. The stringy plant could’ve gotten there by attaching to the propeller of a boat and breaking free when the boat reversed, he said.
“The problem with the invasive plants is that they can really change in a negative way the ecosystem of an area,” Brockettt said. “They change the substrate to make it more mucky and murky.”
Milfoil and pondweed are present at more than 10 locations around Lake Tahoe. Emerald Bay has been one of the largest removal projects. Divers will also be working at Lakeside Beach, the Ski Run Marina, the Truckee River Dam and in the Truckee River this year.
“We’ve really expanded what we’ve done in the last two years,” Brockett said.
Though the program has been successful in Emerald Bay, it takes constant maintenance to keep the weeds from growing back. Each year, though, fewer plants return to the lake floor in areas that have been treated, Brockett said.
“You’re not going to get rid of all of them and they’re going to keep coming back,” he said. “Until we get all of them out of the lake and know that all the seed banks are gone, it will take constant maintenance.”