Marla Bay algae invasion a mystery
August 6, 2008
SOUTH LAKE TAHOE – It’s stringy. It’s bright green. And it’s slimy. Very slimy.
It is algae, and people have found it in the shallow waters of Marla Bay at unprecedented levels this summer, surprising scientists and concerning residents.
“I was so shocked,” said Heidi Archdeacon, a longtime summer resident of Marla Bay. “It’s just grown incredibly.”
The algae’s growth also has surprised scientists at the Tahoe Environmental Research Center of the University of California, Davis.
“Occasionally, you see very small amounts in the water in the lake, but it usually tends to settle,” said Scott Hackley, a staff research associate with the center. “It’s just really striking to see that level of green.”
The algae bloom mostly has settled in the Marla Bay area, just south of Zephyr Cove, Hackley said, but what’s causing the bloom remains unknown.
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“It’s a very open question,” said research center Director Geoffrey Schladow, noting more research is needed to determine the cause of the unusual Zygnema growth.
Researchers hope to determine whether an unknown source of nutrients is sending nitrogen and/or phosphorus into the bay, fueling the growth of Zygnema.
High fecal counts registered in the water near Marla Bay during this year’s Water Quality Snapshot Day could be a potential source of food for the algae, said Dennis Oliver, spokesman for the Tahoe Regional Planning Agency.
Oliver speculated that the high counts could be from horse manure running into the bay or a possible sewer leak.
Researchers hope to examine a possible relationship between the algae and Asian clams, which also have been found in abundance in the area.
Asian clams have likely been in Lake Tahoe since at least 2002, according to an April research center study, which found the density of clams in the lake is higher than ever.
The clams could create pockets of water with relatively high calcium concentrations favorable to invasive mussel growth, Oliver said. The planning agency hopes to retrofit a boat this fall with an underwater vacuum to remove Asian clams from the lake.
A potential link between the clams and algae in Marla Bay remains unverified, though that doesn’t ease Michael Donahoe’s concerns. The Tahoe Area Sierra Club conservation co-chairman says the issues reflect a bigger problem: inadequate management to prevent undesirable species from entering the lake.
“It’s just symptomatic of what’s going on around the lake,” Donahoe said. “We’re not winning this battle right now, and we don’t seem to have the collective will to address the issues.”
Oliver disagreed. “I wouldn’t use these two things to mark the broad effectiveness of TRPA erosion controls and source-reduction programs,” he said.