School's out, and Baltimore's Inner Harbor just got its first report card. The grade: C minus, and that may have been generous.

The grade, for 2012's calendar year, marks the first time the harbor received a complete report card. With eight inches less rainfall than comes down in the average year, the harbor caught a break. With less rain and snow sending polluted runoff into the harbor, the water clarity and quality improved over 2011's numbers. But luck eventually runs out, and the harbor could fail next year's tests if it doesn't do its homework. Its assignment: Take in less trash and figure out how to fix the ailing infrastructure that surrounds it — leaky sewer pipes and a massive stormwater system.

"Stormwater runoff is still the biggest source of pollution," said Adam Lindquist, the Healthy Harbor Coordinator for the Baltimore Waterfront Partnership. "These improvements will be temporary and fleeting if we don't address it."

The city's signature water body has long been one of its most polluted, with high levels of nitrogen, phosphorus, sediment and toxics. It was also one of the most neglected, with civic leaders shrugging their shoulders over the nearly annual summer fish kills, unsightly trash and fetid smell.

But that changed in 2010, when the Baltimore Waterfront Partnership, a business-funded group created to clean up the harbor, stated its goal to make the harbor swimmable and fishable by 2020.

The Partnership decided that, to clean the water, it had to know exactly how dirty it was, and where it needed to improve. So it hired the scientists at Ecocheck, part of the University of Maryland's Center for Environmental Science, to grade the harbor.

Ecocheck has been grading many of the Chesapeake's larger tributaries since 2006. But the harbor proved a different beast. Initially, the team only had monitoring data from one station in the harbor.

Over the last three years, Lindquist has worked with Baltimore Harborkeeper Tina Meyers to build a bigger data set. The harbor cleanup partnership now has 30 sites that it monitors biweekly for levels of nitrogen, phosphorus, dissolved oxygen, chlorophyll a and water clarity.

Lindquist said he'd like to add bacteria to the monitoring list, adding that if it was already on there, "the harbor would have gotten a failing grade."

Already, the Maryland Department of the Environment is considering a plan for a trash total maximum daily load in the harbor, similar to the one in the Anacostia River. City officials are also considering a ban on Styrofoam and a plastic bag fee. Washington, DC, passed a plastic bag fee a couple of years ago, and river advocates there say it has made a big difference in cleaning up the Anacostia.

Despite harbor advocates pressing for action on stormwater, the city seemed poised to pass a stormwater fee that was about 40 percent lower than what was originally proposed. Under state law, Baltimore city and the state's nine most populous counties were to have established a stormwater fee by July 1.

Harbor advocates are optimistic that water quality will improve. Never before, they said, has so much attention been paid to the harbor's cleanliness. In addition to the heft of the business community and new environmental leadership at City Hall, the harbor also has a friend in Blue Water Baltimore, which formed three years ago when five smaller groups merged.

Halle Van Der Gaag, the executive director of Blue Water Baltimore, has been pushing for more stormwater controls, and said she'll continue to do so.

"We need to make sure the work we're doing is actually getting the job done," she said. "For dealing with stormwater, the solution is at our fingertips."