James Johnston was driving over Fountaingrove Parkway late Wednesday when his Dodge Charger hit a deep puddle in the roadway and started to hydroplane.

He quickly let off the accelerator and regained control of the heavy sports car, then noticed what was causing the roadway flooding.

“There were giant pools of water on the road wherever they’d blocked up the storm drains,” Johnston said. “I was all right, but it might have been dangerous for a new driver.”

Concerned that rains will wash pollutants left behind by the devastating Sonoma County wildfires into sensitive local waterways, state and local agencies have raced to place erosion controls and rainwater filtration measures around storm drains.

These include gravel bags and straw wattles installed around hundreds of storm drains where the bulk of the 5,300 homes lost in Sonoma County were located, including the Coffey Park and Fountaingrove neighborhoods of Santa Rosa, the Larkfield-Wikiup neighborhoods just north of the city, and rural areas along Mark West Creek.

City officials say they are trying to strike a balance between filtering rainwater before it hits the waterways and blocking rainwater from effectively draining off local roads. They’ve been aggressively installing the gravel bags and various types of wattles, but are now “taking a step back” to find the best design for the measures.

“We want to maximize the filtration, but we also want to minimize the impact to the roadways in terms of localized flooding,” said Rita Miller, deputy director of environmental service for Santa Rosa Water department.

Miller said she didn’t have any information about how bad the flooding was Wednesday evening, but there were no immediate reports of accidents.

The North Coast Water Quality Control Board in Santa Rosa has been encouraging Santa Rosa to respond quickly before heavy rains arrive. It has rained three times since the fires, with Wednesday night’s precipitation of about an inch being the largest storm yet.

Various groups are stepping forward to offer volunteers and expertise on how to best protect the watershed. Chris Grabill, a member of the Santa Rosa Board of Public Utilities, has been working with the Permaculture Skills Center in Sebastopol and others to see if toxin-cleansing mushrooms can be encouraged to grow in the wattles and take up toxins.

The nonprofit Sonoma Ecology Center in the Sonoma Valley is experimenting with wattles filled with biochar charcoal as another way to absorb contaminants. And the city is doing a pilot project to see if it makes sense to divert runoff to the Laguna Wastewater Treatment Plant, explained Mona Dougherty, a senior water resource control engineer with the water quality board.

“I have read that both have a lot of promise in treating storm water, so that’s great,” Dougherty said.

You can reach Staff Writer Kevin McCallum at 521-5207 or kevin.mccallum@pressdemocrat.com. On Twitter @srcitybeat.