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Water Hyacinth and Water Lettuce Hydrilla

Updated: Nov 27, 2023

What Have We Done About Hydrilla?

Removing hydrilla is extraordinarily difficult and costly. Hydrilla grows faster than manatee can eat it, and whenever a manatee breaks a hydrilla plant, the broken plant fragments can form new plants.

The name “hydrilla” originates from the Latin word “hydra,” which has two different meanings. The first definition of hydra refers to the many-headed beast in Greek mythology. When one head of the hydra is cut off, two grow back. More modernly, Hydra means an evil that can’t be overcome by a single effort. I’d say hydrilla fits both of these definitions.

Hydrilla is known to completely take over waterways and to prevent any navigation by manatee or human. The fact that hydrilla is present throughout King’s Bay is worrisome because if left unregulated, King’s Bay could eventually look like the image above.

In the past, people tried to eliminate hydrilla by poisoning it, which was costly and risky. In King’s Bay, poisoning worked and the hydrilla died, but it made the overall situation worse. As hydrilla died, it sunk to the riverbed and contributed to the thick layer of muck. This muck created an anaerobic environment where rooted plants, like eelgrass, could not effectively survive.

Poisoning, combined with the massive amounts of saltwater that flooded into Crystal River from the No Name Storm on March 13, 1993, led to the death of tons of hydrilla and added to the mucky, anaerobic riverbed.

How To Combat Hydrilla

There are only a few effective ways to prevent devastating levels of hydrilla.

1: Catch hydrilla early. If we notice hydrilla growth early enough, we can prevent if from getting out of control.

2: Manatee eat hydrilla, so if the hydrilla isn’t overwhelming, manatee will be able to graze and reduce hydrilla density.

3: Plant eelgrass properly. Mature and properly planted eelgrass outcompetes hydrilla. If you swim in Kings Bay, you rarely see hydrilla in the main cluster of established eelgrass. You see it around patches of eelgrass, but well established eelgrass outgrows nascent hydrilla.


The fourth and final invasive aquatic plant is lyngbya. Lyngbya, unlike the other plants discussed, is native to Florida. It had been the worst invasive aquatic plant in Crystal River for years, but it can’t tolerate saltwater. As saltwater intrusion increased from hurricanes and the lowering of the freshwater aquifer, lyngbya levels decreased. Lyngbya is now mainly found in Hunter’s Spring.

Lyngbya grows by attaching to other seagrasses and rocks on the riverbed. When mature, trapped gas in the lyngbya mats forces the invasive plant to the surface (see image above). Once on the surface, lyngbya blocks the sun from reaching the native eelgrass on the riverbed. Like the other invasive plants, lyngbya can also be spread in the ballast of a boat.

How To Combat Lyngbya

The most effective way to counter lyngbya is by planting eelgrass. This is exactly what Save Crystal River hopes to accomplish by planting eelgrass. Once the eelgrass matures, it outcompetes lyngbya. This forces lyngbya to the surface prematurely and forces the invasive plant out of the springs. The more eelgrass we have, the less lyngbya we have.

Unlike hydrilla, water hyacinth, and water lettuce, manatees won’t eat lyngbya because it is slightly toxic. This means it’s up to us to make sure our waterways are clear.

While there’s not much we can individually do to eliminate these invasive aquatic plants, be careful not to transfer them to a new waterway. Clean kayaks, boats, paddle boards and any other mode of water transportation before traveling to a new location.

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