CARMEL VALLEY — From the cockpit of a Bull 206 helicopter hovering above the Penasquitos Lagoon, veins of blue water below contrasted with the green wetland.
There wasn’t much green in sight a month ago. Most of the wetland was completely submerged in standing water, leaving the area prime for mosquito breeding. It even prompted concerns over the spread of West Nile Virus.
“There’s less water now and that’s good news,” said helicopter pilot Jason Colquhoun over the roar of the engine. “The view from up here says a lot.”
Colquhoun, who works with the San Diego County Vector Control Program, dropped organic larvicide while cruising over the area. Normally, he treats 20 acres every 28 days in the spring and summer months. But given the proliferation of mosquitoes over the past two months, 70 acres of the lagoon received larvicide spraying.
Amid residents’ concerns, the greater-than-normal aerial application is half of the two-pronged approach to combat the mosquito problem at the Penasquitos Lagoon.
“We’re taking an aggressive approach to fixing this,” Colquhoun said.
As well as the larvicide, the California State Parks dredged the mouth of the lagoon at Torrey Pines State Beach mid-May as a stopgap measure. Reconnecting the lagoon to the ocean let a lot of the stagnant water drain out, significantly cutting down the mosquito population.
Mosquito trap counts at the lagoon dropped from 3,350 the week of May 6 to 327 the week of May 20, according to data from vector control.
The department also reported that the mosquitoes in the lagoon showed no evidence of West Nile Virus.
Three days after the dredging, piles of sand once again blocked off the lagoon. Chris Conlan, vector ecologist with the county, warned that the number of mosquitoes could rise again since the lagoon is plugged.
“The counts can jump really fast,” Conlan said.
That’s why the city of San Diego is looking to open the mouth of the lagoon for the rest of the year with a larger-scale operation. At a cost of $80,000 to the city, the excavation is scheduled to start June 17 and wrap up June 24. The less-intensive excavation last month carried a price tag of about $25,000 and was paid for by state parks.
Particularly in early May, residents and visitors complained about swarms of mosquitoes blanketing the area.
Supervisor Dave Roberts said he’s encouraged by the progress made in the past month. His office has received fewer calls from constituents about the mosquito problem in recent weeks.
Powerful waves and high tides in the winter caused sand to build up, blocking the lagoon. Typically, the lagoon is dredged in early April. So why did it take longer to begin this year?
The Los Penasquitos Foundation has secured funding from various grants for the annual excavation in the past, according to Mike Hastings, executive director of the foundation. This year, the grant money wasn’t enough to pay for the entire operation, so the city of San Diego and state parks signed on to fund a larger portion of the dredge than in prior years. Because a new legal agreement had to be inked between the parties, there was a delay.
“We’re working on a funding mechanism that’s more consistent,” Hastings said.
Adding to the woes: The lagoon choked off earlier than normal this year, likely because there’s currently more sand on Torrey Pines State Beach than previous years, he noted.
But the lagoon closing off from the ocean is only part of the equation, said Darren Smith, an environmental scientist with state parks.
Walking along a trail on the perimeter of the lagoon, he noted that freshwater from Carmel Creek, Los Penasquitos Creek and Carroll Creek feeds into the lagoon year-round, supplying freshwater that allows mosquitoes to breed, he said.
Tidal saltwater promotes fisheries and benefits other kinds of marine life in the area. Yet the inland freshwater has the opposite effect.
“Saltwater lagoons are full of bio-diversity,” Smith said. “You don’t get that with freshwater. Some species can’t survive in it.”
Additionally, the freshwater allows the growth of invasive plants like rye grass, which can be found on the eastern part of the lagoon. Yet it’s slowly marching west.
As development increased over the years, he said more and more runoff has been pumped into the lagoon through the three creeks. He said he’s encouraged by new homes designed to limit runoff, but the problem seems to be getting worse.
“It’s really not helping the health of the lagoon,” Smith said.
As one possible solution, he noted earthmovers could carve out channels in the lagoon so the freshwater has an easier path to the opening — a plan state parks is considering.
“When the water moves there and sits, it’s an issue for a lot of environmental and health reasons,” Smith said.