VIOLA, Mo. -- Four years into a five-year study, researchers investigating pollution in Table Rock Lake have reached a conclusion that raises more questions than it answers.

The lake in southwest Missouri, near the Arkansas line, is too large and complex to track all the factors affecting its water quality. That makes it difficult to determine which pollution-control efforts are working and which aren't.

"If we had as much information as we had on Table Rock, but it was on a smaller lake, we could probably predict and tell you everything you needed," said Dan Obrecht, a researcher at the University of Missouri in Columbia. "But this one is a big puzzle."

Missouri Department of Natural Resources director Stephen Mahfood said his department is working with its Arkansas counterpart to fashion a joint plan for monitoring the lake and other shared bodies of water.

"We're trying to float all the ships and bring the quality of the water up," he said.

Mahfood hopes the agreement will lead to more standardized and useful data about the lake.

The memorandum of agreement with Arkansas "is almost here," Mahfood told the Springfield News-Leader.

The quality of the lake -- which has more than 750 miles of shoreline and 45,000 to 50,000 acres depending on its water levels -- is no small issue for the region.

At the bustling Jug-N-Plug in Shell Knob, Mike Burns sells sporting goods, snacks, liquor and other items to tourists. He's seen the town grow and change in the 19 years he's lived there.

The lake has changed, too.

"I won't even swim in the water any more," Burns said. "When I first moved here, it was pretty blue water. Over the years, it's gotten worse and worse."

Research indicates that because the lake is so deep -- 250 feet in some spots -- it is considered anoxic, or oxygen-poor, although that's mostly confined to the lake's bottom layer.

Over the years, as phosphorus levels increased on the lake and widespread algae blooms clouded the water, water-quality advocates looked for ways to tackle the problem.

Point sources such as the Springfield Southwest Wastewater Treatment Plant greatly reduced their phosphorus levels to satisfy DNR and the Environmental Protection Agency.

But a multitude of nonpoint sources ranging from parking lot runoff, septic tanks, golf courses, farms and over-fertilized yards continue to put nutrients into the lake, feeding the algae.

The long-range monitoring is necessary to find out what's happening in the lake, researchers say.

"We, as a society, tend to be reactive rather than proactive on these types of things," Obrecht said. "It's hard to get people to spend money to be proactive without a guarantee there's going to be a positive outcome."

While too much algae can pose problems, so can too little, said Paul Michaletz, a research scientist with the Missouri Department of Conservation.

Several years ago, algae blooms were blamed for a die-off of bass, one of the fish that draw anglers and help keep the lake economy humming. That prompted Southwest Missouri State University professors John Havel and Russell Rhodes to study how algae behaves on the lake's James River Arm.

During the study, one major change has been the reduction of phosphorus released from Springfield's southwest sewage plant.

"The water has been clearer than it was earlier," Havel said. "What we do not know is if that is due to the reduction of phosphorus or other causes."

Conservation department scientists know intense efforts to eliminate algae from lakes can devastate fisheries, Michaletz said. That happened when several Southern states went too far.

"The fisheries pretty much collapsed because they didn't have enough nutrients to support the fish," he said.

Research sponsored by Table Rock Lake Quality indicated a direct link between septic system pollution and the amount of development in coves. That discovery prompted an effort to get federal funds to find resorts, businesses and homeowners willing to try new technology to treat their sewage.

"Now, we're actually picking sites and have hired a contractor to install those, possibly after the first of the year," said Dave Casaletto, project manager for Table Rock Betterment.

Casaletto is administering an effort to install sewage treatment systems on the lake that are more efficient than conventional septic systems. The group has received about 40 applications and has to decide which ones will qualify for the program.