A cleaner Tampa Bay is sprouting more and more sea grass, a sign that the bay is almost completely recovered from the time, decades ago, when it was a polluted cesspool.
The bay gained 1,745 acres of sea grass between 2010 and 2012, state biologists reported Wednesday, an increase of 5.3 percent.
Tampa Bay now supports 34,642 acres of sea grass beds. That's the largest amount of sea grass measured since the 1950s, according to scientists at the Southwest Florida Water Management District, more commonly known as Swiftmud.
"It's exciting to see the bay recovering like this," said Holly Greening, executive director of the Tampa Bay Estuary Program. "No place else in the United States is showing this kind of recovery."
Swiftmud scientists began surveying the bay's sea grass beds in 1988, redoing their maps every two years. This is the fourth consecutive survey that found gains in Tampa Bay's sea grass.
Tampa Bay is Florida's largest open-water estuary, covering about 398 square miles at high tide.
Sea grasses are crucial to the bay's health because they provide food and shelter for a wide variety of fish and other marine species. They filter impurities in the water and stabilize the bay bottom's shifting sands. To thrive, sea grass needs water that's clear enough for a lot of sunlight to get through it.
In the 1950s and '60s, dredging created land for development around the bay but wiped out much of its sea grass, hurting commercial and recreational fishing. Polluted runoff killed even more sea grass. By the early '90s, the bay had lost 80 percent of its sea grass, more than anywhere else in Florida.
The Tampa Bay Estuary Program, created by Congress in 1991, has been working to cut the pollution flowing into the bay and restore the sea grass to the extent it covered in the '50s. The new survey indicates that the bay is now just 3,358 acres shy of that goal, according to Greening.
Since 2000 the region has cut by some 400 tons the amount of nitrogen pollution flowing into the bay even in normally rainy times.
The cuts required cooperation from business and people from all around the bay area, she said. Power plants cut the amount of nitrogen billowing from their smokestacks and settling on the water. Homeowners cut back on how much fertilizer they put on their lawns.
Middle Tampa Bay showed the largest acreage increase in sea grass with 817 acres, a 10 percent boost. To the scientists' surprise, the largest percentage increase — 73.2 percent, or 612 acres — occurred in Hillsborough Bay, which abuts densely developed Tampa and its industrial port.
"We were down to zero acres there in 1982," Greening said. "Now sea grass covers 1,033 acres."
The increase in sea grass has apparently boosted the population and diversity of fish in the bay, too. "We're hearing from fishermen that the fishing in the bay is better than it's ever been," she said.
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Sea grass generally grows in waters less than 6 feet deep, but in the clear waters around Egmont and Anclote Keys it can be found in water 10 feet deep or more.
In addition to surveying Tampa Bay, Swiftmud checks the St. Joseph's Sound/Clearwater Harbor system every two years. The results there showed a decrease of less than 2 percent, small enough that it could be due to the accuracy of mapping methods.
Craig Pittman can be reached at email@example.com