HUDSON – Teenagers from all over New England will spend the next month investigating every aspect of Pushaw Lake to answer a question that’s older than they are: Where is the phosphorus pollution coming from?

Pushaw Lake has struggled with high phosphorus levels for more than three decades. And despite efforts by local residents to fix leaky septic systems and discourage broad, treeless lawns, the levels have only been rising over the past five years.

“There are some places where [development] is just door-to-door. [The lake] is pretty stressed,” said Jeff Hayward of Old Town, who spends summers at a family camp on the shore and is active in the Greater Pushaw Lake Association. “There’s enough [phosphorus] now to support an algae bloom.”

The 5,000-acre lake’s natural amber hue, caused by its high mineral content, could be the lake’s salvation since it filters sunlight and limits the out-of-control algae growth that clogged the lake in 1970.

But it’s just a matter of time before the equilibrium shifts – and more nutrients could make the shallow lake even more vulnerable to algae and invasive aquatic plants, Hayward said.

Phosphorus pollution originates from septic systems, runoff from fertilized lawns and even soapy waste water. Most often, it adheres to soil particles and rides into a lake or pond by way of erosion. But many of these sources have already been addressed on the lake.

While captaining a pontoon boat across the lake’s shore Friday, Hayward pointed out a shrubby lawn, landscaped to stabilize the soil.

“Three years ago, that was just grass down to the shore … people don’t realize,” he said.

This month, 37 students from all over New England will be taking water samples, walking the streams that run into Pushaw Lake and working in university laboratories to help Hayward in his effort to protect Pushaw.

The students, ages 16 to 18, are all attending a summer-long residential program based at the University of Maine and centered on science and math. The program is an offshoot of Upward Bound, a federally funded effort to expose bright kids from blue-collar families to college life.

The idea is to get the kids out of their textbooks and into real-world science, where questions are far more numerous than answers, said Nate Larlee of Thorndike, the math and science program coordinator.

“Science is deciding what we do know, and what we don’t know,” he said Friday. “We’re teaching them to ask questions.”

Lowering a Secchi disc over the side of the boat to test the lake’s clarity Friday, the students crowded around to peer at the black-and-white circle, watching it fade beneath the waves.

“Can you see it?” asked one.

“Really, are you sure?” cried another.

“You can still see it? Oh wow.”

“Mind if I try the scopey-ma-jig?”

These kids come from rural Maine, east Boston and everywhere in between.

They aspire to gynecology, electrical engineering, biochemistry and zookeeping, and they’ve taken part-time jobs and extra classes to help them along their way.

They actually have conversations about plant reproduction methods, and they’re working on independent research with college professors and graduate students.

“It’s exciting to see how they get the point,” said Ling Huang, a Ph.D. candidate in computer science at Orono and a second-year instructor in the program.

For more information about Pushaw Lake and the efforts to control phosphorus, contact Laura Wilson of the University of Maine Cooperative Extension at 581-2971 or Jeff Hayward at 827-6536. For more information about Upward Bound’s Math and Science Program, call Nate Larlee at 581-3720.