Rob Mitchell’s commute has taken him over the Presumpscot River in Westbrook for the past 15 years.

But when he took up kayaking about 10 years ago, the river started to look different to him.

In it, Mitchell saw the potential for a recreational water park — a project he thought he’d take on once his kids graduate from high school.

Last summer, he found out he wouldn’t have that much time. He learned that Sappi Fine Paper was facing a deadline to build a fish passageway at its dam at Saccarappa Falls — where he envisioned placing the water park’s main attraction. Although his son is just finishing his freshman year, Mitchell is pushing the project forward now.

“A light bulb goes off. Boom. This has to happen today,” he said Monday.

Sappi is currently building a fishway at the Cumberland Mills Dam, just downstream from the falls, as ordered by the Department of Inland Fisheries & Wildlife. Once that opens — the deadline is May 2013 — the company has two years to build the fishway at Saccarappa Falls.

Mitchell would like Sappi to build a passage that would allow fish to travel upstream over the dam and kayakers to travel downstream over the falls. Using his own money, he hired an engineer last fall to draw up the design.

The plan calls for construction of a narrow channel from the top of the falls through an existing island in the river and exiting into the main waterway just before it reaches the bridge at Bridge Street.

In addition to the channel, which could be used for kayaking and tubing, the park would have trails and terraces for spectators along the riverbank. A trail already crosses a bridge to the island.

“This is a very grand plan,” acknowledged Mitchell, 47, who lives in Raymond and owns HVAC Services Inc. in Westbrook.

Still, he believes the project would cost under $3 million — less than the cost of the type of fish ladder that Sappi is building at Cumberland Mills, he said.

But he hasn’t convinced the company.

When Mitchell met with Sappi officials last year, he said, they told him his idea wasn’t possible. The company reiterated that Monday.

“(We) do not believe the proposal is feasible given the complex regulatory environment governing hydroelectric stations,” said a statement from Sappi.

Mitchell believes more people calling for the water park might change the company’s position.

“No one’s going to tell 100,000 people they’re wrong. Nobody,” he said.

Last week, Mitchell launched a Facebook page showing the conceptual drawing of the park, and he’s been handing out stickers promoting a website, westbrookriverpark.org, that he expects to go live within a couple of days.

He plans to speak about the project later this month before the Westbrook-Gorham Chamber of Commerce and will have a booth at the Westbrook Together Days celebration on the first weekend of June.

Mitchell has already talked to some local groups, such as the Westbrook Environmental Improvement Corp.

Victor Chau, a city councilor and member of that group, said it’s too early to say whether the committee can support the project.

“It sounds like an interesting idea, but of course we need more information,” he said.

The Friends of the Presumpscot River has taken much the same position, said Dusti Faucher, a member of the group’s board.

“It’s still an idea at this point, and the idea is wonderful,” she said.

But the group would not want construction of the park to delay or impede fish passage at Saccarappa Falls, which the group has long fought for, Faucher said.

Even if the project gets Sappi’s support, the plan would need approval from the Federal Energy Regulatory Commission, which licenses hyrdroelectric dams.

The license currently calls for the fishway to be built as a ladder or a lift, Faucher said. FERC would have to agree to reopen the licensing process to allow for the type of passageway that Mitchell proposes, said Sean Mahoney, director of the Conservation Law Foundation.

That process would likely be lengthy and complex, which could be problematic considering Sappi’s May 2015 deadline to have a fish passage operating at Saccarappa Falls.

“I think it would be very difficult to try to change course at this point,” Mahoney said. “Does that mean it’s impossible? No.”

Staff Writer Leslie Bridgers can be contacted at 791-6364 or at: [email protected]