A surprising culprit has been fingered in the Case of the Mysterious Vanishing Lake:

November.

Monitors installed at White Bear Lake to help sort out the reasons for its dramatic decline in recent years have established that "a tremendous amount of water leaves the lake in November," said Paul Putzier, project manager for the Minnesota Department of Natural Resources.

"It shocks me that it's that much," he said.

The effort to trace evaporation off the surface month by month is part of a major, multiyear series of studies aimed at diagnosing the reasons for the drop in lake levels.

Much is at stake. The Metropolitan Council has invoked the potential need for hundreds of millions of dollars in spending to pipe and treat surface water across the north metro from the Mississippi River, if it turns out that underground sources are being depleted.

White Bear lakefront owners have suggested that the well digging to support nearby suburban sprawl, which brings lots more thirsty lawns among other things, may be sucking the lake dry.

As scientific studies proceed, examining the many ways in which water can arrive and depart, progress is quietly being made on other fronts:

• A report is being prepared for state lawmakers in the coming legislative session as to what it would take to artificially augment lake levels.

"There've been a number of estimates," Putzier told northeast metro water officials at a recent gathering, "and we're trying to get a solid sense of what that would take if someone wants to provide the funding."

• The White Bear Lake Conservation District has reported to the DNR precisely what elevation the lake needs to reach in order to be adequate for lake users.

"The district is asking the state to consider placing the protected lake level about 925 feet" above sea level, said Bryan DeSmet, who chairs the district's Lake Level Resolution Committee. "The basis for that was historic safe use of the lake [for boats for instance], beaches being open, that kind of thing."

A settlement agreement in a lawsuit over the lake's condition calls for an elevation to be established in about a year.

DNR Section Manager Jason Moeckel said the issues to be addressed will include not only swimmable beaches and other recreational uses, but fish and wildlife, the shoreline slope, and the vegetation. "We're trying to take it all into consideration," he said.

A huge surprise amid all the work taking place was provided by the evaporation study, Putzier said.

Many factors involved

The state has just finished two seasons of monitoring White Bear Lake water levels, he said, and "a lot of factors are involved, including precipitation and water exiting related to pumping … But evaporation turns out to be a big factor as well."

Officials are hoping to have monitoring stations on the lake next year to observe it under differing conditions, he said, and "beyond that we'll have to scavenge for money. Three years in a climate cycle is not long."

The assumption had been that evaporation peaked in warm months, and indeed a "big blast happens in summer," Putzier said. "But then in November, too, the lake functions as a huge heat sink, and when drier, cooler air sweeps across the lake, a lot more water vanishes."

As part of its study, the state is appealing to folks living nearby for any record they've kept of when the lake freezes over. Many lake owners record dates when the ice goes out each spring, but seldom do they record when the lake ices over.

DeSmet, an environmental engineer, said the bottom line is that anxiety over White Bear Lake is driving basic research that will improve understanding of lakes in general.

"We know as much about our lakes as the money available to find out," he said. "Until we get a driver [that is, a strong motivation] to spend more money and gather good data, it just doesn't happen.

"The fact that so much of our population growth has gone to wellsversus surface water has had a big impact. The more we know, the better we can manage the resource. But no one asks unless there's a crisis."