The District’s four-year-old tax on disposable bags has been a rousing success, leading to a 60 percent drop in household bag use and many fewer plastic bags littering city streets. Such are the claims of city environmental officials, citing surveys done by an independent research firm last year.

City revenue figures, meanwhile, show no continuing decrease in the use of disposable bags. In fact, bag tax collections have proven remarkably stable since the nickel-per-bag fee debuted in January 2010.

The tax has generated $150,000 to $200,000 a month for the District’s river cleanup efforts, but the steady collections throw into doubt claims that the tax has overwhelmingly succeeded in pushing down bag use over time, as backers had predicted.

That hasn’t stopped officials from touting the success of the tax. “Since the law took effect in 2010, District businesses have seen a dramatic reduction in bag usage and environmental cleanup groups are reporting fewer bags polluting D.C. waterways,” a city release stated.

Keith A. Anderson, director of the D.C. Department of the Environment, said the survey “confirms the significant progress the District is making toward reducing plastic bag litter and restoring health to the Anacostia and Potomac Rivers and their tributaries.”

The polling commissioned by the environmental agency and conducted by the research firm OpinionWorks reached 600 city residents and 177 businesses. About two-thirds of respondents said they had noticed fewer plastic bags littering the city since the tax went into effect. Residents estimated they used significantly fewer disposable bags — an average of four a week today, compared with 10 a week pre-tax — and businesses reported providing significantly fewer bags to customers.

Yet tax collections don’t support the idea that bag use has dropped dramatically. In between the District’s 2012 and 2013 fiscal years, bag tax revenue grew by about $12,000 — a half-percentage point rise that represents well over 200,000 additional bags.

Yesim Yilmaz, chief of revenue estimation for the District’s Office of the Chief Financial Officer, said the revenue trend was a surprise.

“When we forecasted the bag fee collections back in [2009], at the time the city adopted the fee, we had expected that these collections would decline over time,” she said. “But they did not.”

According to the original estimates, the city was expected to collect $1.05 million in fiscal 2013, which ended Sept. 30. Instead, it collected in excess of $2 million.

Brian Van Wye, who manages stormwater programs for the Environment Department, said several factors could explain why bag tax revenue has been stable while residents report using fewer bags, including the District’s recent population growth and the openings of several new grocery stores. He also credited increased city outreach and enforcement of the bag-tax, causing more businesses to remit bag-tax revenue that has been used to clean and restore waterways.

“Having said that, [the city]’s objective is not to collect fees; instead, our objective is to change behavior in ways that will, over time, restore health to our waterbodies and make them fishable, swimmable resources for District residents, businesses, and visitors,” he said in an e-mail.

One issue with the city’s recent survey is that it relied on poll respondents to estimate the number of bags they used or gave to customers before the tax went into effect, which could cause some to overestimate the actual change in their behavior and create an unreliable baseline for pre-tax bag use.

There is strong evidence that bag taxes do reduce bag use. A September dissertation from a Princeton University graduate student, recently highlighted by the Brookings Institution, studied bag habits in the District and Montgomery County, concluding that the five-cent tax was very effective in curbing disposable-bag use. (A five-cent credit for using reusable bags, on the other hand, was not.)

That academic research is backed by reports from clean-water groups that fewer plastic bags are fouling the Anacostia River and other city waterways. The survey reported similar impressions from residents and businesses.

Yilmaz said it’s “hard to say why” the collections haven’t dropped, despite the survey findings and anecdotal evidence. While the use of bags may be stable or rising in absolute terms, she said, the rate of disposable-bag use could be declining when factoring in the city’s rising population and incomes.

Bag-tax revenue has risen and fallen alongside general sales tax revenue to a strong degree, even though a major driver of disposable-bag use — groceries — is not taxed. That could indicate a correlation between bag use and overall retail activity.

While the economic consequences of the bag tax remain unclear, the political implications are mostly settled at this point, the polling found: Less than one-fourth of the residents surveyed felt bothered by the law. The rest said they supported it or had no opinion on it.

Business owners, who reported saving money on bags, were even more supportive, with only about one in 10 expressing objections.

A Washington Post poll conducted in January 2010 found that residents then were almost evenly split on the bag tax.