Armed with pitchforks, Stacy McGaha and Pat Willging climbed into a canoe Saturday, ready to do battle with an invasive plant growing along the edges of upper Bayou St. John, not far from Lake Pontchartrain.

At first glance, the water hyacinth doesn’t look frightening. It floats on the water, with waxy, round leaves over buoyant roots. In the springtime, it bears attractive lavender blossoms. Although native to the Amazon River basin, it was introduced to the United States as gifts to visitors who stopped at the Japanese pavilion at the World Cotton Exposition held in New Orleans in 1884-85.

But it’s destructive.

“I’d call it the feral hog, or maybe the rat, of water plants,” McGaha said, citing how easily the plant multiplies and the damage it can cause.

Elsewhere in Louisiana, Willging has seen waterways jammed full of hyacinths. “If we let it go, the bayou will be impassable in the summertime,” she said.

Neighbors say that water hyacinths hadn’t been able to flourish in Bayou St. John until recently because of the bayou’s higher salinity level. The bayou had been largely blocked from the lake’s regular flow by a waterfall dam beneath Robert E. Lee Boulevard that was removed in January 2013.

Today, the bayou’s salinity mirrors that of Lake Pontchartrain, a brackish lake where salinity can shift quickly due to wind direction, rainfall and water from the rivers and channels that empty into it.

And because New Orleans’ wet weather, salinity levels now are low, making conditions perfect for water hyacinths. “All of this rain, they’re loving it,” said Bob Thomas, who directs the Loyola Center for Environmental Education and chairs the sustainability committee at City Park.

Sara Howard, 40, and Sonny Averett, 43, a wife-and-husband team who run a tour company called Kayak-iti-Yat, frequently paddle through this part of the bayou, in the shadow of Holy Trinity Greek Orthodox Cathedral. Last fall, they first noticed patches of water hyacinths that had grown in recent months.

So Howard helped to organize Saturday's work group. Weather permitting, another group will hack away at the plants on Tuesday, she said.

Last week, Howard also did a quick scan along the bayou on the south side of Filmore Avenue and found a few water hyacinth plants there. So it’s multiplying, she said with a grimace.

The problems the plants cause go far beyond bothering canoeists. When floating water hyacinths cover the surface of any body of water, they block sunlight to submerged water plants and creatures, depleting the water of oxygen and asphyxiating fish.

So, on Saturday morning, Howard, Averett and a few dozen other New Orleanians spent the morning fighting water hyacinths. Some stood on the river bank, pulling at the plants' furry roots, which were intertwined with beneficial vines along the shore. Others boarded canoes and kayaks and pulled at the plants from the water, herding the green leaves and roots into piles for transport to a nearby truck.

Curtailing the spread of this invasive plant felt urgent to Bywater resident Adam Karlin, 36, who came with his wife, Rachel Houge, 39, and their toddler Sanda. “We’re out here to be good neighbors to the city,” he said. “But also because the city doesn’t seem to be doing anything.”

In years past, the city tried to fight the hyacinths, but there was never enough money to fight them consistently in a tropical climate with a year-round growing season, Thomas said. “You have to stay on it all the time. Nobody is willing to give that money,” he said. 

Given that context, “volunteers are really important,” Thomas said.

Thomas recalled how Jean Lafitte National Historical Park and Preserve used to drive machines that looked like floating combines through the bayous in its Barataria unit, in an attempt to control the plants that were choking the waterways.

The LSU Ag Center has helped to stem the growth of another invasive plant, giant salvinia, by breeding insects that will eat the plants. The AgCenter maintains several weevil nurseries and distributes the insects to areas with giant salvinia infestations.

To date, there’s been no similar development for water hyacinths. Though some insects will slow the species' growth, many of the state’s nature preserves and parks still use herbicides to combat the plant.

Manual removal of the hyacinths is a necessary but never-ending task, said Natalie Robinson, 38, the membership coordinator for the Friends of City Park, who helped to coordinate the disposal of the plants in the park’s compost area Saturday.

Robinson knows the plant well, because some sections of the park also are plagued by it. “You’ll never get rid of it. Because once you touch it, pieces of plants break off and its seeds spread,” she said as she pulled out yet another hyacinth plant from the bayou’s bank.

A few feet away, Stacey Rogers, 50, noticed with delight some green crabs in the water, a sign that some creatures known to inhabit the lake are also living in the bayou. 

Averett also likes what he has seen in recent years, after the dam was removed. He sees both freshwater fish, like bass and bream, but also speckled trout and redfish, which prefer more brackish and salty water.

The City Park staff is also looking closely at Bayou St. John, which connects to the park’s lagoons in a few places, Thomas said.

The Lake Pontchartrain Basin Foundation has been monitoring water quality in the lagoons, tracking salinity levels.

And, Thomas said, even though City Park’s new golf course has pledged to follow "green" standards, scientists are watching closely to ensure that it doesn’t harm the water with herbicides or fertilizers.

“We must do this. Because we know that we live in an estuary and that everything is connected,” Thomas said. “It’s a delicate balance.”