How clean is clean enough? That's the question raised recently over the effort to rid the Anacostia River of the mountains of trash littering its banks and waters.

The Natural Resources Defense Council argues in a lawsuit filed last week that the trash "pollution diet" on which the Anacostia has been for the last six years is destined to fail.

That’s because the plan that directs trash removal efforts for the three Washington, D.C. area jurisdictions in the river's watershed does not set a specific limit on the amount of trash it can handle while maintaining water quality, the environmental nonprofit said in a suit filed Sept. 19.

Rather, the total maximum daily load (TMDL) approved by the U.S. Environmental Protection Agency in 2010 only states how much trash must be removed or prevented from entering the heavily urbanized Potomac River tributary each year.

“It doesn’t set a maximum load, so it’s missing the ‘M’ and the ‘L’ in TMDL,” said Becky Hammer, staff attorney with the NRDC’s water program. “The reason a maximum limit is established is so plans like this can have a fixed target for measuring progress. If you don’t have that, you’re left with a paper exercise that lacks real world accountability.”

When it was established, the plan used a baseline estimate of the amount of trash that was entering the river around 2010 — about 1.2 million pounds, or 600 tons. It required the three jurisdictions that drain into the Anacostia -- the District of Columbia and Maryland’s Prince George’s and Montgomery counties -- to remove their share of that trash tally each year. That would, at least in theory, result in a nearly trash-free river.

But the NRDC’s suit argues that the overall estimate of trash entering the river was based on limited surveys, making the figure both inaccurate and quickly outdated as the region’s population grows. A one-time baseline does not account for above-average trash years, Hammer said, when removing a few hundred tons of trash would still leave plenty floating downriver.

Food wrappers, plastic bottles and foam containers floating down the river or collecting on its shores can be hazardous to fish and wildlife and​ impair public recreation in the waters

The Anacostia was the second river in the country to be declared impaired by trash, following the Los Angeles River, whose “zero trash” TMDL took effect in 2007. Twenty-two California cities sued over the notion of being responsible for every piece of litter that entered the river, but the courts upheld the river’s pollution diet requirements.

At the end of 2014, Baltimore joined the list of trash-impaired waterways, when the Maryland Department of the Environment approved a TMDL for the Inner Harbor and its two tributaries, the Gwynn Falls and Jones Falls. As with the Anacostia’s TMDL, Baltimore’s requires the city to remove a certain amount of trash per year based on estimates of how much is already entering the waterways. Some Baltimore environmental groups likewise opposed that concept, insisting that the standard should be zero trash entering the water, within a reasonable margin of error.

Hammer said one of the reasons the NRDC is suing about the Anacostia plan now, six years after it was put in motion, is that jurisdictions like Baltimore are following its example and adopting similarly toothless TMDLs.

Terri White, a spokeswoman for the EPA, wrote in an email that the agency does not comment on pending legislation.

Adam Ortiz, director of Prince George’s County’s department of environment, which is charged with complying with the Anacostia TMDL, said the current plan has done plenty to get trash out of the river. Under it, his county has to remove or prevent hundreds of thousands of pounds of litter from entering the river’s tributaries each year.

“The trash diet gets us much farther along,” Ortiz said. “Is it perfect? Nope. But it represents tremendous advancement.”

According to the 2010 TMDL, Prince George’s County has to remove or prevent the lion’s share of trash from entering the river -- 695,000 pounds per year, including what’s removed by federal facilities, known pollution sources and the highway administration. For Montgomery County, that number is 325,000 pounds per year, and for the District of Columbia, 243,000 pounds per year. These totals include a 5-percent “margin of safety.”

While many TMDLs -- often called "pollution diets" -- set a maximum for a given pollutant, trash TMDLs call for 100 percent removal of an estimated "baseline" amount of trash. The Anacostia plan states that, “unlike most,” its total loads are expressed in terms of what must be removed or prevented from entering the water body, rather than a total of what the river can handle while maintaining water quality.

A large part of the trash reduction effort in the Maryland counties entails preventing litter from entering the waterways — or being produced in the first place. Both Maryland counties and the District have passed some version of a ban on the use of polystyrene, commonly called Styrofoam, in making food and other product containers. Montgomery County and the District also require retailers to charge a fee for plastic bags, which are often found in the river.

The TMDL gives the jurisdictions some credit for passing these bans, but quantifying their actual impact is tricky. A Styrofoam ban alone won’t ensure their recyclable or compostable alternatives don’t end up in a gutter, so it doesn’t necessarily reduce the total weight of trash a jurisdiction is contributing.

Ortiz’s department said the Metropolitan Washington Council of Governments has established a work group to vet the credits given these preventive measures in the TMDL.

NRDC’s Hammer said not having a reliable method for measuring the success of preventive programs — but crediting them anyway — is another weakness of the plan.

“What we have is a situation where all three jurisdictions in the watershed are spending a lot of time and effort coming up with math formulas for guessing how much trash they’re keeping out of the Anacostia,” she said.

The NRDC wants to see the TMDL rewritten to establish a zero tolerance for waste, unless evidence shows that some amount can be discharged while still maintaining water quality in the river. As more urban areas consider the need for trash limits in their waterways, Hammer said these first few plans serve as de-facto examples that need to be strengthened.

Ortiz said the trash diet has done plenty to keep trash out of the waterway, even if there’s room for improvement. “We can split hairs on ideas, but overall this is a tremendously good thing for our waters and for our urban neighborhoods,” said Ortiz.