On the surface, Old Tampa Bay north of the Courtney Campbell Causeway looks fine.
Kayakers paddle about the mangroves, anglers work the flats for trophy tarpon and water scooters skim the Philippe Park shoreline at Safety Harbor.
Below the surface: not so good.
Even though the Tampa Bay system's overall aquatic health is the best it's been in 60 years, the northern expanse of Old Tampa Bay is a cause for concern, ecologists say.
Seagrass fields, essential to a robust estuary system, are lagging. Persistent algae blooms have tainted the water with an oily terra cotta-colored slick for three of the past four summers. A troubling layer of muck near Safety Harbor is getting bigger and deeper.
The situation has reached critical mass, and the Tampa Bay Estuary Program is spearheading a three-year study to identify problems north of the Courtney Campbell Causeway.
The far-reaching evaluation and assessment of water quality will begin this fall and be conducted by Janicki Environmental, a St. Petersburg consulting firm. The study, funded largely through a $1.2 million grant from the Southwest Florida Water Management District, will take a look at nutrient influxes, hydrologic changes and water circulation patterns and how all that affects the natural flush of the northern reaches of Old Tampa Bay.
It's a priority, said Nanette Holland O'Hara, spokeswoman for the estuary program.
Overall, she said, the lower part of the Tampa Bay system is in pretty good shape.
The southernmost part of the system is Tampa Bay. It is bounded on the north by an imaginary line between Picnic Island in Hillsborough County and Papys Point in Pinellas County — roughly defined by the Gandy Bridge. It measures 225 square miles. Old Tampa Bay is the area north of the Gandy, about 75 square miles.
The entire Tampa Bay system, which includes McKay, Hillsborough and Old Tampa bays, is the state's largest open-water estuary and covers nearly 400 square miles.
"Water quality is as good as it was in the 1950s," O'Hara said. "We have as much seagrass as we did back then. But the one big problem is the area of Old Tampa Bay above the Courtney Campbell.
"We've had some persistent water quality problems there, including big algae blooms over three of the past four summers, some of which had spread throughout Old Tampa Bay down to the Gandy Bridge," she said.
"We also have an area of really nasty gooey mucky sediments near Safety Harbor and Oldsmar," she said. The muck has been there for a decade or more and appears to be spreading, she said.
"This study is intended to take a really thorough look at what's going on in that part of Old Tampa Bay," she said.
Inadequate flushing likely is the problem, she said.
Before the Courtney Campbell Causeway was built, a natural circulation of water cleansed the upper reaches of Old Tampa Bay. Since then, the only large connection to the lower part of the bay is the bottleneck under the center span of the causeway bridge. The rest is blocked by the causeway, she said.
"There is a circulation problem," she said. "Water does not flush out of that part of the bay as quickly as the lower part" of Old Tampa Bay.
The likely solution: When road work is planned for the Courtney Campbell Causeway, engineers should consider installing more culverts or small bridges to allow the upper sections of Old Tampa Bay to flush properly, she said.
The only Florida Department of Transportation projects involving the Courtney Campbell Causeway in the next five years are the construction of a bike path from Pinellas County to the Ben T. Davis Municipal Beach and a resurfacing project, according to the department's website.
All the speculation on flushing and fixes has to be confirmed through science, O'Hara said. Any recommendations will be based on what comes out of the study.
"We don't know for sure," O'Hara said. "We just know we have a problem there, and chances are it will not get better unless we look at long-term solutions."
"Estuaries like Tampa Bay, where saltwater and fresh water mix, are nurseries for young fish, shrimp and crabs," states the estuary program's website. "More than 70 percent of all fish, shellfish and crustaceans spend some critical stage of their development in these near-shore waters, protected from larger predators that swim the open sea."
Capt. Mark Newton, who runs the Fun Flats Fishing charter service, has fished Old Tampa Bay for more than a decade. He said that sometimes during algae blooms, the live bait he throws into the water north of the Courtney Campbell dies long before fish bite.
He said he is concerned mostly about the algae blooms, which are happening more frequently.
"I've been running charters up there for the past 12 years," he said. "And for the past three or four years, we've started having that orange algae bloom. It looks like Orange Crush." This year, he said, the algae plume stretched south to the Howard Frankland Bridge.
That punches into business, he said.
"I've learned that when it gets real bad, I have to get out of the area," he said. "I try to fish areas where the water is cleaner."
There are other consequences, he said.
"We used to have tremendous mackerel runs up there before this," he said. Since this apparent algae bloom problem, the mackerel have not been there, he said. "They just haven't shown up."
Capt. Nick Angelo owns the Shallow Water Fly Fishing charter service and knows that when the algae bloom surfaces, he has to hunt fish elsewhere. As a fly fisherman, he motors around looking for fish to cast to, and he can't do that if the visibility in the water is low.
He said the condition likely is due to inadequate water flow. The area near the Courtney Campbell is clear, but the shoreline from Tampa to Oldsmar to Safety Harbor is murky, he said.
"It's definitely not good," he said. "It's wild. During the summer, you can't see anything because the water is too dirty."