Jim Waymer

FLORIDA TODAY

MOUNT DORA – Vinh Le untangles silvery fish one at a time from his net.

His arms and shoulders ache from yanking up his two nets, each as long as several football fields. It’s his first day on the job.

“I’m absolutely tired,” Le says in exhaustion, as his boat drifts in the middle of a pea-soup-green Lake Apopka.

These are "rough" fish hardly anyone eats. And they're a tough haul for the 54-year-old Apopka man. But his harvest helps perform some heavy ecological lifting to revive what once was the most polluted lake in Florida. Le and about a dozen other fishermen chip away at two chemical killers — nitrogen and phosphorus, which are overloaded in the lake. Each gizzard shad’s body weight is 0.8 percent phosphorus, mostly in their bones, derived from the fish's food sources in the lake.

Net a million pounds of shad annually and that's 8,000 pounds of phosphorus out of the lake. Each pound of phosphorus can grow 500 pounds of algae. So that's 4 million pounds of potential algae per year out of the way of bottom grass, bass and other coveted lake life.

This week, the St. Johns Water Management District wraps up its annual gizzard shad harvest — a unique program that teams government and businesses to extract the nutrients that fuel fish-killing toxic algae blooms. The program helped cut Lake Apopka's nitrogen and phosphorus levels in half over the past two decades. It's a direct, cheaper way to remove the two algae-fueling nutrients from Florida waters where shad reign supreme, especially compared to stormwater projects, sewer plant upgrades or septic tank removals. And it proves that sometimes just getting the shad out can be a vital piece of the ecological restoration puzzle.

"The lake has really rebounded remarkably," Dean Dobberfuhl, a bureau chief at the water management district, said this recent day out on a placid Lake Apopka. "In terms of a restoration technique, it's very cheap."

The district's program has removed almost 25 million pounds of gizzard shad from Lake Apopka since 1993, reducing nitrogen and phosphorus levels in the lake by more than half, in combination with other nutrient reduction methods.

The program typically removes about 1 million pounds of shad from the 31,000-acre lake annually.

Fertilizers from Lake Apopka's surrounding farms and homes feed algae blooms that cloud sunlight to bottom plants — vital nurseries for bass and other important sport fish. Waters low in nitrogen and phosphorus are clear, a tad tea-colored, and team with underwater plants that fish need to feed, breed and hide in.

So to restore those healthier conditions, government gets fishermen to strip out a "junk" fish that's native to Florida but often an opportunistic pest.

Shad fan a vicious cycle in some Florida lakes: Algae-laden water with fewer bottom plants yields fewer sport fish and more gizzard shad. Typically, only 5 to 20 percent of the fish are gizzard shad in a healthy lake. But when nutrients go haywire, so do gizzard shad, which can reach upward of 90 percent of of a lake's fish.

That's when things get real messy.

Gizzard shad graze on algae and other bottom gunk, stirring up sediments and further clouding water, blocking sunlight to bottom plants that sport fish rely upon.

And Florida's algae situation seems to have worsened in recent years, heightening the need to remove excess nitrogen and phosphorus.

A state report released late last year found half of Florida's lake surface area with elevated levels of chlorophyll, a hallmark of algae. Blooms are fed by rising nitrates from farm and residential fertilizers, sewage, pet waste and other human-related sources, the report found.

Report: Half of Florida lakes' surface have 'elevated' algae levels

A century of onslaught for Lake Apopka began in the 1890s with construction of the Apopka-Beauclair Canal, which lowered the water level by a third. But in the 1930s, the lake still had bountiful bottom plants and gamefish.

Beginning in the 1940s, farms eventually would swallow 20,000 acres of wetlands along the lake’s north shore, removing natural water filters. Before the 1980s, surrounding communities discharged wastewater into the lake, as did citrus processing plants. Until the late 1990s, farms sent phosphorus-rich water there, too.

With few bottom plants able to grow, sportfish all but vanished.

The district put the lake on the road to recovery by buying up surrounding farmlands and restoring them to marsh, filtering lake water through wetlands and removing gizzard shad.

In the early 1990s, more than 53 metric tons (86 percent) of the 62 metric tons of phosphorus loading into the lake annually was from farms. The rest came from the atmosphere (8 percent) and other sources (6 percent).

But since then, phosphorus into the lake has been reduced by more than 80 percent, to 11 metric tons, including the 90.7 metric tons of phosphorus removed directly from the lake in the past two decades via the shad harvest. That prevented an estimated 45,360 metric tons of potential algae growth.

The 'net' effect

Currently, Lake Apopka and Lake George in the St. Johns River, northeast of Ocala National Forest, have gizzard shad harvest programs. But the district also has harvested the fish from lakes Griffin and Denham in central Florida and at Newnans Lake east of Gainesville.

Phosphorus levels decreased by half and algae by 70 percent after only three years of experimental shad harvesting from Lake Dunham in the 1990. Sportfish soon rebounded.

The district contributes $675,000 a year to to subsidize commercial shad harvesting, paying $605,000 to fishermen and $70,000 to an independent entity for monitoring and verification of the fish collection.

The district is nearing the end of a 3-year contract with Raffield Fisheries, Inc., of Port St. Joe, to process and handle the harvested shad. Raffield pays independent fishermen 27 cents per pound. The fishermen get a rare exemption to the state's ban on nets that entangle fish by the gills. But the district monitors the harvest closely to make sure the fishermen don't kill too many other types of fish, most of which must be thrown back. They can keep gar and tilapia but must toss all gamefish back.

The shad are frozen at Raffield's processing facilities, then sold to crayfish farmers as crayfish food or bait to commercial crabbers, or deposited in a landfill. Most of the fish sold by Raffield are transported to Louisiana.

The water management district subsidizes the shad harvest because there's not much of a local market for the distasteful fish. There have been attempts to make the shad into cat food or develop recipes to make them more palatable.

"Nothing worked very well," said Jim Peterson, field program supervisor with the district's bureau of water resource information. "There's no real human markets we could find."

One key clue to success in Lake Apopka is the strong rebound of eel grass and turtle grass — key nursery habitats for fish.

Peterson steers a district boat close to Lake Apopka's shoreline, where thick grass blades poke up from the bottom.

"This is all new growth," he says as birds cackle from nearby trees. "It's great fish habitat."

Submersed plants grew from near nothing in the late 1990s to 48 acres by 2015, according to district data.

Report: Half of Florida lakes' surface have 'elevated' algae levels

The more bottom plants and the fewer shad, the healthier the lake grows.

So each shad that Vihn Le and others net out brings the lake closer to a much clearer future, biologists say.

This day, the lake glistens a pea-soup green, from a surface as smooth as glass, as Le's boat floats near the lake's center.

Wearing orange rubber gloves, his arms weary, Le flops each shad into brown plastic bins, clearing up the water one "rough" junk fish at a time. Standing in the water management district's boat, Dobberfuhl describes how over time, each shad removed adds up to a lake reborn.

"We think it's had a pretty profound effect on the lake and its water quality," Dobberfuhl said.

Contact Waymer at 321-242-3663 or jwaymer@floridatoday.com Follow him on Twitter@JWayEnviro and at facebook.com/jim.waymer