Tampa Bay now supports 40,295 acres of sea grass beds, the largest amount of sea grass measured since the 1950s, a new study by scientists at the Southwest Florida Water Management District has found.The extent of sea grass beds is a way to measure the water quality in the bay. The more sea grass there is, the cleaner the bay is."Sea grass was our canary in the coal mine (and) major losses occurred when Tampa Bay was in distress," said agency scientist Kris Kaufman, who led the study. "Now with sustained good water quality in the bay, sea grasses are flourishing."This increase in sea grass, announced Wednesday by the agency commonly called Swiftmud, has surpassed the baywide recovery goal of 38,000 acres set 23 years ago by the Tampa Bay Estuary Program when the bay was suffering from serious pollution problems.In other words, water quality in the bay is now as good as it was in 1950, explained Holly Greening, director of the estuary program."This is a remarkable achievement, made even more so when you consider that the bay region has grown by more than 1 million people in the last 15 years," Greening said. "This kind of environmental recovery is a living testament to the collective efforts of all of us working together — the cities and counties, the private sector and the citizens who treasure the bay."Tampa Bay is Florida's largest open-water estuary, covering about 398 square miles at high tide. It's important both for the bay area's environment and for its economy.Sea grasses are crucial to the bay's health because they provide food and shelter for 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 and sewer plants that dumped untreated waste directly into the bay 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. That was disastrous for life in the bay.In 1991, Congress created the Tampa Bay Estuary Program, which has since been working to cut the pollution flowing into the bay and restore the sea grass. By then the dredge-and-fill work and sewage dumping had been eliminated, and the biggest problem remained nitrogen pollution, primarily from runoff. The estuary program's staff worked with local governments and businesses to cut that back, too.Meanwhile, Swiftmud scientists have been documenting the sea grass growth in estuaries along the Gulf Coast since 1988. They began seeing a strong return of the sea grass beds in the bay, and this year saw gains in every part of the bay, including a 47 percent increase since 2012 in Old Tampa Bay, which stretches from the Gandy Bridge north to Oldsmar and east to Tampa. Water quality there has tended to lag behind the rest of the bay.The return of the sea grass beds does not mean the ban on harvesting oysters and scallops from the bay has been lifted. The shellfish ban is based on the detection of harmful bacteria. Lifting that ban requires a decision by the state Department of Agriculture and Consumer Services, said Nanette O'Hara of the estuary program.Contact Craig Pittman at [email protected] Follow @craigtimes.