Aside from a noisy pair of mallards, it was a tranquil morning at Neacham Bay on the east side of Lake Coeur d’Alene.
Mellow strains of jazz drifted from an aluminum fishing boat, where Idaho Department of Environmental Quality employees were collecting and processing water quality samples.
The early snowmelt sent the monitoring crew out onto the lake this week to track the flow of sediment and historic mining pollution into the lake from tributaries.
“It helps us understand how the lake changes with the seasons, and how the big spring runoff affects the lake’s chemistry,” said Craig Cooper, a lake scientist for DEQ.
He and two co-workers sampled sites at the northern end of the lake, where the current carries muddy, metals-rich water from the Coeur d’Alene River. On Thursday morning, they zeroed in on Neacham Bay, a long, narrow water body surrounded by luxury lakeside homes, where they spent 2 ½ hours taking samples.
“The bays tell us a lot of interesting things,” Cooper said. “They may provide us an early glimpse of how the lake is changing due to natural and human causes.”
Since the 1990s, Lake Coeur d’Alene’s overall water quality has improved. However, monitoring over the past five years shows dissolved oxygen levels dropping in parts of the lake’s northern end.
That’s raised red flags for DEQ and the Coeur d’Alene Tribe, because oxygenated water acts as a cap on mining pollution at the bottom of the lake. More than 75 million tons of sediments there are tainted with lead, arsenic, cadmium and zinc. The metals washed downstream from Idaho’s Silver Valley during a century of mining activity.
Five years ago, the state and the tribe shook hands on a deal to avoid a Superfund cleanup of the lake. Instead, they agreed on a plan to keep water quality high, with dissolved oxygen providing a barrier against the metals becoming suspended in the water.
So, seeing a five-year drop in oxygen levels is like watching your blood pressure creep up, and wondering what’s going on with your health, said Laura Laumatia, the tribe’s lake management plan coordinator.
“We’re all concerned about the dissolved oxygen, because that’s really the crux of the lake management plan,” she said. “We want to spend the next year understanding what’s causing the changes.”
Sampling bays is part of that effort. They’re shallower than the rest of the lake, and their water quality is more vulnerable to impacts from recreation and development.
“You get a more detailed understanding of human interactions with the system,” said DEQ’s Cooper.
Neacham Bay was picked for monitoring not only for the homes surrounding it, but because of the density of buildings above it. “It’s one of the more developed bays,” he said.
On Thursday morning, Cooper and his co-workers anchored the 26-foot-long aluminum boat in the bay and set up a floating laboratory. Rigorous protocols, including frequent changing of plastic gloves, are followed to ensure the integrity of the water samples taken.
“We work too hard for bad data,” said Bob Witherow, a DEQ technician.
The samples will provide a snapshot of the bay’s oxygen, temperature and metal levels. They’ll also impart information about the bay’s levels of phosphorus, nitrogen and phytoplankton, which forms the basis of the lake’s food web.
The Hewes Craft boat was purchased two years ago with settlement money from Avista Utilities and Hecla Mining Co.
“No taxpayer dollars went into it,” said Glen Pettit, a DEQ technician.
It has more room than DEQ’s old research boat, and a covered area keeps ice from forming on the deck during the winter. The monitoring crew spends about 90 days on the lake each year.
Cooper keeps business cards handy to give to boaters who pull up and have questions about the monitoring. But, “most people ask us how the fishing is,” he said.
The crew will be out again next week, chasing the plume of metals and sediment from the spring runoff as it moves around the lake. Tracking how the water circulates in Lake Coeur d’Alene is also part of understanding what’s happening with oxygen levels.
“It’s a cool, complicated lake from a science perspective,” Cooper said.