But even that mediocre rating, to be issued Monday at an Inner Harbor press conference, comes with a big asterisk, as the report card's compilers note that rainfall last year was far below normal, reducing the amount of pollution washed off city and suburban streets, parking lots and yards.
"It's not as peachy as it might look," said Heath Kelsey, manager for EcoCheck, an ecosystem health rating program run by the University of Maryland Center for Environmental Science. "It's the lowest C you can get - it's really hovering around the D-plus to C-minus range."
Moreover, the water-quality grade doesn't factor in the trash, sewage and toxic sediments that make the harbor generally unsafe for swimming or for consuming many of the fish that can be caught in the Northwest and Middle branches of the Patapsco River.
Those involved in developing the report card acknowledge that a C-minus grade might be seen as okay, if not good. But they note that even with favorable weather the harbor's overall water quality was only acceptable 40 percent of the time.
"Most people if they got a 40 percent (score) would not think of that as a C-minus," said Tina Meyers, the Baltimore Harbor Waterkeeper who helped compile the report card. "If you used standard school grades, it would be F's all the way to 60 percent."
But organizers said water quality is graded on more of a curve so it can reflect changes in degraded water ways like the harbor.
"It's going to be perceived as a good grade," said Adam Lindquist, Health Harbor campaign coordinator for the Waterfront Partnership. But he noted that despite Superstorm Sandy late in the year, 2012 was the driest for this area in five years, with just 34.31 inches of precipitation, compared with the annual average of 42. "We can't rely on dry weather to improve the harbor's grade indefinitely," he said.
Lindquist said he found it a little surprising that the Inner Harbor's water quality actually was a little better than the Middle Branch, as measured by levels of algae, nutrient pollution, clarity and dissolved oxygen for fish to breathe. But the Middle Branch came out much better on bacteria levels, an indicator of the risk of getting sick from contact with the water.
Bacteria levels from sewage leaks and storm runoff were not factored into the water-quality grade, but were scored separately. Even with relatively little rainfall, levels in much of the Inner Harbor met the safe-swimming standard less than 60 percent of the time, based on sampling taken by Blue Water Baltimore. A few spots in the wider mainstem of the Patapsco actually measured safe every time they were sampled.
"I think it shows what hope there is to clean up the habor if people can reduce the amount of stormwater coming off their property," Lindquist said, "because it shows what we can achieve in drier weather."
The report card did not include any grade, though, for two of the harbor's more entrenched problems - the trash fouling its shore and water, and toxic contaminants in the bottom sediments. Compilers said they did not yet have a good way to measure those, or the resources to do so.
The report card's authors say efforts appear to be increasing to deal with the trash and sewage leaks reponsible for high bacteria levels, especially in dry weather. The city reported sweeping 9,989 tons of litter off streets last year, for instance, a 39 percent increase over 2011. And the city has formed a WatershedStat task force to tackle the widespread sewage leaks, Lindquist said. City crews are focusing first on identifying and fixing all the leaks responsible for sewage getting into the harbor from the Linwood Avenue storm-drain outfall, he said.
Even so, much more needs to be done, campaigners say, including the adoption of meaningful fees on storm-water runoff and measures to curb litter. Baltimore City Council is still weighing its fee schedule, which must be adopted by July 1 under state law. Statewide legislation that would have mandated a fee on plastic merchandise bags and a nickel deposit on beverage containers both died in Annapolis this year.
"I think it's too soon to show any real trends in the health of the harbor," said Meyers. But she called the report card "a good first step," saying it was the product of more extensive water-quality sampling and other data than any previous evaluation.