After more than 20 years of paddling the Hillsborough River, Joe Faulk knows when somebody has been using fertilizer upstream of his Canoe Outpost.
"The water hyacinth and pennywort seem to bloom overnight," said Faulk, the only canoe outfitter on the river. "I can always tell when the water even gets a small dose of nitrogen."
But as of June 1, at least some of that threat has been removed due to a new Tampa ordinance against selling or using lawn fertilizer during the summer rainy season. Advocates know it's not a panacea for the river's problems, but it's one more step in a long fight to save a river that has nearly been split in half by decades of development.
"Even if only half of the people comply with the ordinance, that will mean about 8 tons of nitrogen that won't end up in the river," said Nanette O'Hara of the Tampa Bay Estuary Program. "That will make a huge difference."
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The Hillsborough, one of Florida's most popular paddling rivers, begins in the Green Swamp, east of Dade City. It flows for 59 miles through Pasco and Hillsborough counties before emptying into Tampa Bay in downtown Tampa.
Most of the upper river runs through public lands managed by the state, county or the Southwest Florida Water Management District, and as a result, has remained mostly pristine.
But for decades, the lower end, particularly the stretch through Tampa, has looked more like a northern industrial river than a wild Florida waterway.
"People just wrote it off," said Phil Compton of the environmental group Friends of the River. "It was abused and forgotten, sort of the back alley of Tampa."
Compton points to three factors that contributed to the lower river's decline: hardened shoreline, low water flow and nitrogen-rich suburban runoff.
"We have done a lot to get rid of the seawalls and re-create natural shoreline," he said. And due to a citizen-inspired lawsuit against government regulators, "the river is getting steady flow 365 days a year."
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Lawn fertilizers have been a persistent problem for the river and Tampa Bay. The nitrogen in fertilizer fuels algae blooms, which give the water a greenish tint. The discolored water blocks sunlight, which impedes the growth of sea grass, an important habitat for marine creatures.
And when the algae die and decompose, that robs the water of dissolved oxygen, leading to fish kills.
Tampa's new ordinance is nearly identical to Pinellas County's, which went into effect in June 2011. Numerous municipalities in the area have similar residential bans.
The new regulations restrict the use and sale of landscape fertilizers containing nitrogen from June through September, when almost-daily summer rains can wash the residues into the river and the bay. And the rest of the year, when it is legal to sell and use fertilizers, at least half of their nitrogen must be in a slow-release formulation.
Opposition has come from large commercial fertilizer companies, some lawn care services and homeowners who want lush lawns, regardless of what fertilizer runoff can do to the environment.
Compton and other advocates say that the benefits of the ordinance far outweigh any drawbacks.
"This is going to improve the health of the waterway, which will increase real estate values,'' Compton said. "The Hillsborough River is Tampa's No. 1 natural and economic resource and you could see this as an investment in the city's future."
Compton said Tampa Bay anglers will also enjoy the benefits of the summer fertilizer ban because of how it will help fish habitats.
"Trying to grow sea grass in a bay full of algae is like trying to get a house plant to grow in a dark corner of a room," he said. "It is just not going to happen."
O'Hara said the key to the program's success will be public education.
"Once people begin to understand that what they do in their yard will have an impact on the water where they paddle, fish, swim and boat, we will begin to see a difference," she said.
Faulk, who paddles the Hillsborough every day, said the river's health will be improved by everyone who follows the rules.
"The prescription is simple," he said. "Stop feeding it and it will heal itself."
Contact Terry Tomalin at firstname.lastname@example.org.