These nutrients come from many sources.

Water discharged from the Flathead Valley's sewage treatment plants. Fluids oozing from the area's septic tanks. Fertilizers for crops and lawns. Nitrogen-laden smoke from forest fires and from people burning trees to clear some woods.

Many nutrients get filtered out on their way to Flathead Lake.

But a lot of nitrogen and phosphorus reach the lake.

The amounts in Flathead Lake have increased in uneven spurts by an estimated 10 to 20 percent since the late 1970s, said Ric Hauer, a University of Montana professor of limnology who does research at the Flathead Lake Biological Station at Yellow Bay.

These nutrients feed phytoplankton, which are part of the lake's algae. Phytoplankton gobble up oxygen in the lake.

Right now, Flathead Lake is a beautiful crystal blue.

But if oxygen levels drop low enough near the lake's bottom, a chemical reaction will kick in to release several decades' accumulation of phosphorus trapped in the mud. The lake absorbs about 135 tons of phosphorus annually. That released phosphorus will boost the growth of algae, which sucks more oxygen out of the water, which releases more phosphorus from the mud.

Over and over and over again.

And Flathead Lake would be swamped with green gunk.

How many extra nutrients are needed to trigger this effect is unknown. How long will it take to trigger this scenario is unknown.

"We are a long way from

this, but we don't want to come close," Hauer said.

Federal laws are in place to prevent this from happening. Those laws require a limit to be put on the volume of nutrients that the Flathead River can carry into Flathead Lake - and in countless similar situations across Montana and the United States.

The laws have been in effect for many years.

But Montana is a few years away from setting a limit on nutrients flowing from the Flathead River into Flathead Lake - and with rivers and lakes elsewhere in the state.

"It's never been done [in Montana] and it's highly controversial. So it's been slow," said Gary Root, Columbia Falls sewage plant supervisor.

That's because it will cost millions of dollars to upgrade each Flathead Valley sewage plant to help meet those yet-to-be-determined limits. A major chunk of that money inevitably will come from higher monthly sewer bills.

Figuring out where to place rural homes and septic systems - and how many should be allowed - will become much trickier. Even people's habits in caring for their lawns and fields might have to change.

In 2000, an environmental organization, the Friends of the Wild Swan, won a federal lawsuit that declared that Montana was not setting nutrient limits as required by the oft-amended 1972 federal Clean Water Act.

The Friends of the Wild Swan meet annually with the U.S. Environmental Protection Agency to monitor the state's progress on setting these standards. The state's efforts have improved since the mid-1990s, said Arlene Montgomery, the organization's program manager.

No one will say this outright, but interviewed officials hint that if Montana and its local governments don't adequately control the amounts of nutrients reaching rivers and lakes, the federal government will step in to calculate the goals and enforce the rules.

So far, the state has done some preliminary research on nutrient sources - essentially saying several exist. Now the state has begun to try to nail down specific limits on nutrients entering rivers, and then into lakes.

Collecting raw information for the Flathead River and Flathead Lake likely will take until 2008, said Jim Bond, senior water quality planner at Montana's Department of Environmental Quality. After that, no timetable has been set on crunching the numbers and mapping out plans to reach those goals.

Mystery numbers

This legal compliance situation has seriously spooked local health, public works and sewage-plant officials.

It will be a few years before anyone knows what the legal limits will be on nutrients entering Flathead Lake from the Flathead River.

Those mystery numbers will further split into fractional quotas allowed from numerous sources upstream.

Some natural nutrients will flow into the Flathead River from the river's forested North, Middle and South forks.

When the Flathead River flows past Columbia Falls, that town's aging sewage plant will be allowed to add an unknown amount of nutrients.

No one knows how big a nutrient load that a proposed 1,000-house subdivision at Hungry Horse will add to the river upstream of Columbia Falls. That project plans to add its own sewage treatment plant - similar to a sewer district in unincorporated Bigfork - which also will face tight controls on its discharges into the Flathead River.

Nutrient-laden septic fluids from numerous rural homes - close to and far away from the river - will seep into Flathead River as it flows south. No one knows the quantities and concentrations of the nitrogen and phosphorus in these fluids oozing into the river.

The Whitefish River - carrying discharges from Whitefish's sewage treatment plant - runs into the Flathead River. No one knows how much nitrogen and phosphorus the Whitefish plant will be allowed to release.

Farther south, the narrow Ashley Creek runs into the Flathead River with all of the discharges from Kalispell's sewage plant. That means Ashley Creek is another stream where a still-unknown limit will be put on nitrogen and phosphorus.

More unknowns include questions on how many of the nutrients entering the river come directly from nature. Forest-fire smoke contributes nitrogen, but no one knows how much nor how to control it. Another unknown is how to track the nutrient contributions of farm and lawn fertilizers.

As Joe Russell, public health officer for the Flathead City-County Health Department, put it: "When you're putting together a list of things you can control, it's not a long list."

City plants face first impact

Whether they like it or not, city sewage treatment plants probably will be the first and most expensive spots to be overhauled to cut back on nutrients headed from the Flathead River Basin to Flathead Lake.

That's because these plants are the only places where it is easy to measure nitrogen and phosphorus discharging into the rivers.

And these are the easiest spots to build something that produces visible results.

"When the municipal guys say they're the low-hanging fruit, they are the low-hanging fruit," Russell said.

Officials in Kalispell, Whitefish and Columbia Falls argue that their cities will shoulder the biggest burden in combating nutrients headed for Flathead Lake - despite the strong likelihood that the towns contribute a fraction of all the nitrogen and phosphorus.

Their other complaint is that upgrading sewage treatment plants - adding extra basins, scrubbing equipment and gunk-eating bacteria - will cost vast and yet-unknown amounts of money.

That's because no nutrient limits for individual plants will be nailed down for a long time.

Lewis & Clark County - including Helena - is the Montana metropolitan area farthest along in getting the state to set nutrient limits for its sewage plant. Lewis & Clark's deadline to finish calculating those limits and to map out a fix-it plan is 2012. That implies Flathead County and Montana's other major towns won't have their improvement plans approved until later.

"Anytime you're talking a wastewater plant upgrade, you're talking millions. … We could spend millions and millions of dollars taking the entire step, and still not accomplish what we're supposed to," said Greg Acton, Whitefish's utilities supervisor.

"In a small town, that's huge," Whitefish Public Works Director John Wilson said

Columbia Falls' Root said: "What we're afraid of is that we do this, and the state'll come back to say we didn't do it good enough."

Towns facing major sewage plant improvements would like to get money from federal and state grants.

But the most likely source of the needed millions of dollars is bond sales, officials said, with higher municipal sewer rates needed to pay them off.

Kalispell will be Flathead County's first city to expand its sewage treatment plant - doing so before it will know that nutrient limits it will face.

Kalispell's plant is operating at 90 percent to 94 percent of its current capacity of 3.1 million gallons of sewage a day. Three major housing proposals have recently surfaced that could add another 2,110 homes to Kalispell. And that doesn't count several other proposed rural subdivisions that want to hook up to the city's sewage system.

Kalispell's government expects to soon put out bids to expand its sewage plant by 2008 to be able to treat 6 million gallons a day - enough to absorb several years of a growing population.

If the price tag doesn't exceed $12.5 million, Kalispell's government believes it can tackle the improvements without raising sewer rates.

The X Factor: The current improvement plans have a big blank spot in designing nutrient-limiting upgrades.

"There are so many variables involved. This is an item of significant concern to us," said Jim Hansz, Kalispell's public works director.

Hansz is frustrated that Kalispell is designing its plant expansion to exceed all the current standards on nutrient-laced discharges, and can still fall short if new limits are adopted in a few years.

Meanwhile, Columbia Falls and Whitefish are waiting until the new nutrient standards are set before upgrading their plants.

Neither plant currently trims nitrogen. But neither facility's state permits requires it to do so - yet.

The Columbia Falls plant is more than 20 years old and needs some routine upgrades and expansion to handle that town's growing population. The estimated bill would be $3.5 million to more than double its 350,000 gallons-per-day capacity, without adding in the nutrient-related improvements.

Whitefish's plant - which has been routinely upgraded every few years - is operating at 60 to 70 percent of its 1.3 million gallons-per-day capacity.

Nutrients come from many sources

Montanans love the state's wild and rural nature.

That's why many - especially in Flathead County - stay out of cities to live in the country.

Rural Montanans still tinker with nature, which sends subtle ripples through the environment - including affecting the amount of nutrients seeping through the ground.

One example is smoke. Forest fires are a significant contributor to nitrogen and phosphorus floating through the air to settle on the Flathead River and Flathead Lake. But so are fires that people set to clear brush and trees to create open spaces.

And smoke's role is nothing to sneeze at. The Flathead Lake Biological Station has estimated that 1 percent to 40 percent of the lake's annual 135 tons of additional phosphorus arrives through the atmosphere. The percentage shifts with fire and weather conditions.

People also build homes right at the shorelines of rivers and lakes - and frequently chop down the natural vegetation to create fertilized lawns, said Caryn Miske, executive director, and Mark Holston, public information officer for the Flathead Basin Commission.

Septic tanks near stream banks increase erosion, sending nutrient-heavy dirt toward Flathead Lake.

The roots of natural vegetation do a much better job of filtering nutrients than lawns fertilized with nitrogen and phosphorus that are quickly washed to the aquifer by the extra water needed to grown lawns.

Holston said: "We have to get people to buy into a different aesthetic."

Reporter John Stang may be reached at 758-4429 or by e-mail at jstang@dailyinterlake.com