It’s not exactly a drop in the bucket, but the placement of some 10 million baby oysters in the Severn River this past week was just one piece of a larger effort to help restore the Chesapeake Bay.

The oyster spat hauled from the Horn Point Oyster Hatchery outside Cambridge on Monday were the first batch of a total of 50 million to be placed in the oyster sanctuary outside Annapolis in the coming weeks.

The project is a cooperative effort between Oyster Recovery Partnership, the Severn River Association, the Maryland Department of Natural Resources and Horn Point — but also the public, who donated approximately $27,000 to help the local river group pay for half of the oysters laid on the river bottom Monday.

“Our river and creeks are hurting,” said Lynne Rockenbauch, Severn River Association president. “To make sure we can fish and swim in our river and creeks, we need to take action now.”

Bob Whitcomb, Oyster Committee chair for the association, said Monday’s event “proves private citizens support our restoration efforts and will donate to buy oysters to plant on our reefs.”

“We plant about a million oysters a year. But this is a big push we are proud of,” Whitcomb said.

The Severn was chosen for a few reasons. Salinity levels vital to oyster development are sufficient. The bottom, especially in the nine sites spread across 13 acres of river, was “planted” with crushed rock by the U.S. Army Corps of Engineers in 2010, providing an optimal base for the spat to flourish.

Of the 50 million spat to be planted about 2.5 million are likely to survive to become 3- to 5-inch mature oysters.

Shocking, but that’s normal, said Chris Judy, director of the DNR Shellfish Division.

“People say that mortality rate is high, but it’s typical. If you are a very small vulnerable spat to make it to 3 or 5 years old is a challenge. A lot of things can kill you along the way.”

That is one reason the site will be monitored to determine the mortality rate and whether a second planting, which occurs on many oyster beds, is in order.

“We strive to do our best to monitor all of our plantings,” said Ward Slacum, the Oyster Recovery Partnership’s director of the program. “We will check right after we put them in to understand short-term survival and also several years later to understand what it still there.

“It’s adaptive management,” he said, “and it also determines whether a second planting is necessary”

Then it is up to timing and funding to see if a second planting is possible, he added.

Oyster restoration efforts like Monday’s Severn River project are a key ingredient in wider Chesapeake Bay recovery efforts.

The ability by oysters to filter and clean water is a major factor in the push to grow more oysters on reefs across the bay and in its tributaries. A mature adult oyster can filter up to 50 gallons a day.

But just as important is the ecosystem a thriving oyster reef creates.

“As they grow, they attract other creatures. You are not just getting oysters you are getting worms … mussels, barnacles, mud crabs, blue crabs,” Judy said. “As important as the filtering is the improvement of the bottom ecology, The living reef they make is crucial to marine life.”

As such it is not likely that the successful development of flourishing oyster reefs will clean the bay in and of themselves.

“They are a vital ingredient. But it also about land use, how you manage your garden and lawn, how you fertilize it and farmers doing their part,” Judy said.

Yet it is an important cog in the wheel of bay health.

“The sites we planted today between the two bridges were planted a decade ago with substrate by the Army Corps and could build up a viable population to filter the river and develop valuable marine life for other species,” said Stephan Abel, executive director of the Oyster Recovery Partnership.

“They are critical to have,” he said, “and every tributary should have viable oysters.”

pfurgurson@capgaznews.com