Invasive plant threatens livelihoods in Colombia’s largest coastal wetland

Lean over the side of a small speedboat in Colombia’s Caribbean wetland and, in recent months, the scene has changed from open water to thick mats of bright green vegetation. Residents in and around the Cienaga Grande de Santa Marta say the invasive aquatic plant Hydrilla verticillata has spread quickly since about mid-2025, choking fishing routes and complicating movement in remote communities that depend on the lagoon for day-to-day survival. “What we’re seeing here today is a problem. One that affects not only movement or fishing, but the community as a whole,” said Jhon Cantillo, a local environmental and social leader from the wetland.

Cantillo and other residents describe the plant as hard to remove because it grows dense above the water and sends long strands deep below, with roots reaching toward the lagoon bed. In Nueva Venecia and Buenavista—two fishing communities built largely on wooden stilts over the water—people say swaths of open water have become covered. The change has disrupted routes used to fish, to travel between homes and businesses, and to access fresh water, with residents reporting rising costs for families that increasingly must buy potable water.

For fishermen, the impact is visible in daily work. One small-scale fisherman in Nueva Venecia was pulling dried strands of the vegetation from nets in the sun, after saying the plant has made work impossible. “We can’t work because of this plant,” said Santander Cueto, 61. “It doesn’t let us cast our nets — everything gets tangled.” Demóstenes Guerrero, 58, a fisherman and representative of a fishing association in Buenavista, described the lagoon as increasingly closed off: “The lagoon’s completely covered. There’s nowhere left to fish.”

In some areas, residents have responded by cutting narrow “lifeline” passages through the densest vegetation so canoes can pass without tangling propellers. Those efforts, residents say, are labor-intensive and largely community-driven, and have to be repeated every few days as the fast-growing plant closes routes again. The wetland itself spans about 428,000 hectares (1,600 square miles), roughly the size of Los Angeles, and has been a UNESCO biosphere reserve since 2000.

Experts and local authorities also point to environmental conditions that can accelerate invasive growth. A water and sanitation engineer working in the region, Julián Arbelaez, said the Cienaga Grande de Santa Marta is fed by the Magdalena River, which carries untreated wastewater from across much of the country. Arbelaez said that influx brings nutrients such as nitrogen and phosphorus and can create conditions for rapid plant growth when water slows in wetlands, describing the process as eutrophication. Residents say the plant is also cutting off access to cleaner water sources because many typical routes by boat to freshwater channels connected to the Magdalena River have become blocked.

Local leaders say the crisis intersects with other existing environmental pressures, including changes in water flow and the presence of another invasive aquatic plant, Eichhornia crassipes, which floats on the water’s surface. They also say shifts in freshwater distribution have affected areas where saltwater previously helped suppress or reduce Hydrilla verticillata. Sandra Vilardy, a professor at Universidad de los Andes who has a doctorate in ecology and has worked in the region for about 20 years, said research on how the plant arrived remains limited and that current explanations are hypotheses. She said one likely pathway is maritime transport, with the plant potentially entering through major river systems and then spreading into wetlands through smaller vessels and dredging activity, while she described the aquarium-plant release hypothesis as less likely given local environmental conditions.

Residents and community leaders say the response so far has been slow and insufficient. Cantillo said attempts to remove the plant can also worsen the situation because fragments can break off and spread further. Residents describe removal efforts as focused on small-scale manual clearing by fishermen and sporadic pilot actions by authorities, with no effective large-scale solution in place. The crisis has led some residents to consider leaving, with Cantillo warning, “We now face a risk that we didn’t have 20 or 25 years ago — the risk of mass displacement.”

Officials and some local institutions, meanwhile, describe monitoring and removal efforts underway, alongside regulatory gaps. Alfredo Martínez, director of CORPAMAG, the regional environmental authority, said Hydrilla verticillata is not officially classified as an invasive species in Colombia and that national guidelines for its control are still pending. He said monitoring and removal are being carried out with local community involvement and added that no further expansion has been observed since March, while lower water levels may be slowing the plant’s spread. Even so, community leaders say the problem is reaching nearly every part of daily life, arguing that if fishing cannot continue, commerce and social activity follow.

César Rodríguez Ayala, a community leader in Nueva Venecia, said the effects extend beyond fishing and into the broader economic and environmental fabric of the communities. “If the fisherman can’t work, the shop doesn’t sell,” he said. “We are living a very difficult situation, economically and environmentally.” He said communities want to be seen and helped despite their isolation: “We are part of Colombia too. We live on the water, but we also deserve to be seen — and helped — in a moment like this.”