Kahi Pacarro grew up near the Ala Wai Canal and, like so many of Hawaii’s youth, paddled up and down its length with his canoe club. And like most of them, he knew better than to let too much of the water splash on his skin.

Pacarro now heads Sustainable Coastlines Hawaii, a nonprofit initially formed for clearing trash from beaches until the focus switched to attacking the problem at its source.

“The solution isn’t in cleaning beaches but raising awareness about consumer habits,” he said.

Sustainable Coastlines Hawaii is part of a recent push to find a solution to the Ala Wai mess. It has explored a solar- and water-powered “trash wheel” invention that has been tried in Baltimore to clear rubbish from its harbor.

Other ideas have been raised over the years, ranging from cultivation of oysters or other bivalves that are capable of filtering the dirty water, to an experimental platform using the power of a plant to do the cleansing.

The Ala Wai, now the focus of renewed attention, is a place long thought in need of a makeover. The state Department of Health does not keep water quality data on the canal. But the agency has posted numerous signs along the 2-mile length of the man-made waterway, warning the unsuspecting away from taking a casual dip in it. Most kamaaina already know that would be a bad idea.

And the recent International Union for Conservation of Nature (IUCN) World Conservation Congress held right near its banks fueled the determination of some community leaders to get the job done. A student-led design initiative to distill some of the best ideas is in the planning stages (see story, Page E4).

The Ala Wai watershed encompasses approximately 19 square miles, fed by multiple sources, principally Manoa, Palolo and Makiki streams. The canal was built in the 1920s to drain the wetlands of Waikiki and enable development.

As a flood control structure, it hasn’t been without mishap. The canal overtopped the channel and flooded Waikiki in November 1965 and December 1967 storms, and again during Hurricane Iniki in 1992. More storms flooded the watershed: Manoa Valley in October 2004, causing $85 million in damage; and Makiki in March 2005.

But now another concern looms as large as the worry over flooding itself: the impact of what’s deposited into the canal on its water quality. Among the most notorious contributing factors is effluent — famously the 2006 rains that overwhelmed sewers and forced a wastewater release into the canal. And there have been other sewage spills in the years since.

Urban uses upstream have resulted in erosion and the deposit of sediment and pollutants downstream in the canal and, ultimately, in the marine environment. Such conclusions come from the U.S. Army Corps of Engineers, noting not only that clogging of the streams increases the flood risk, but that pollutants leach into the water.

“As a result, the watershed supports some of the highest levels of contaminants in the nation,” according to the Army Corps’ online summary of the Ala Wai Canal Project, citing a listing under the federal Clean Water Act.

“The coral reef ecosystems in the nearshore waters, including the Waikiki Marine Life Conservation District, are also threatened by these land-based pollutants.”

The project includes a feasibility study and environmental impact statement for work that includes “investigating and evaluating solutions to environmental degradation and flood damage problems throughout the entire Ala Wai watershed.”

There’s been no small amount of work in the search for solutions. The state Department of Land and Natural Resources commissioned an engineering report on a system of flushing the canal, a document published in February 2015.

The conceptual design involves a “sediment basin and water quality marsh” on the Ala Wai Golf Course to contain much of what comes down in stream flow. The flushing system envisioned would pump up groundwater through a well and then discharge it into the canal at its Diamond Head end to improve water quality.

All of this might not have been necessary if the original design of the canal had been realized — but that plan came with its own downside, too. Bob Sigall, who writes a historical column for the Honolulu Star-Advertiser, recounted how the 1926 construction of the canal “drained the swamps of Waikiki and allowed our $11 billion tourism sector to thrive.”

Initially, Sigall wrote, the plan was to extend the canal through Kapiolani Park and have it open to the sea near the Waikiki Natatorium. The Rotary Club of Waikiki in 1967 proposed to adapt that concept, creating a lake in the park and then locate the exit channel.

But the adapted extension would cut through either the Kapahulu Library or Jefferson Elementary School properties, neither of them a good option. Perhaps the plan’s most fatal flaw was the realization that currents would drive trash onto Waikiki beaches.

In more recent years there have been discussions about less drastic cleanup strategies for Ala Wai Canal. Researchers have contemplated cultivating bivalves such as oysters for their capacity to filter the water, an enterprise that has been tried in Baltimore Harbor.

And more than a decade ago, a homegrown solution has been tested, one utilizing the native groundcover plant akulikuli. Dr. Wenhao Sun was the principal investigator for a company called Marine Agritech in a pilot test of a floating platform seeded with the plants.

Sun said he and his partners secured a grant for $500,000 from the U.S. agricultural and defense departments. They chose areas, including by the golf course and other points fed by the streams, to erect the platform.

“Our main target was clarity: reduce turbidity, bacteria, reduce nitrogen and phosphorous, heavy metals,” he said — and it was largely successful.

”The water is brown, and then if you look at it it’s crystal clear, like tap water,” he recalled.

The data are there, but it would take money to implement such a project for the long term, Sun acknowledged, and so far there haven’t been any takers.

Pacarro, meanwhile, is hoping Sustainable Coastlines’ vision can be realized. The organization hired Clearwater Mills, a Maryland consulting group, which on Oct. 20 published its feasibility analysis of the “waterwheel powered trash interceptor.” That’s been tried in Baltimore, as well.

The writers of the report asserted that the wheel would be more effective than the containment boom system installed in Ala Wai Boat Harbor by the state.

The organization is applying for an Army Corps permit and securing its funding, Pacarro said. The full initiative will involve education of the community about keeping trash from entering the streams to start with, he said.

“We want to be proactive to show consumers what is coming down the pike,” Pacarro said. “It’s meant to be a short-term solution regarding the debris, but a long-term solution related to behavioral change.”