FAQs: Hydrilla Treatments on Lake Toho

(Updated 04/25/11)

Media contact: Joy Hill, 352-258-3426;
Patricia Behnke, 850-251-2130

Background: Lake Tohopekaliga, better known as Lake Toho, is a part of the headwaters of the Everglades and is known for some of the best fishing in the country. The lake contains large amounts of hydrilla, a plant that provides food for a nonnative species of apple snail. The snails are the primary food source for the endangered (Everglades) snail kite. The FWC is involved in the management of this lake, which includes continually controlling the growth of hydrilla.

What is hydrilla?

Hydrilla is a nonnative, submersed plant (go to http://plants.ifas.ufl.edu/node/183 for more details).

Why does hydrilla growth need to be controlled?

Hydrilla, a nonnative species, can grow so thick that it causes flood-control problems, shades out native plant species, and can suffocate fish by lowering oxygen levels below its dense canopy. Hydrilla control is important for maintaining the fish and wildlife habitat that supports the fishery, and for maintaining boat channels and fishing access for tournaments and other local tourism.

The FWC strategically controls hydrilla in important areas of the lake every year to allow fish and native species of plants to thrive, to allow water to flow quickly when heavy rains occur, and to maintain boat access into and throughout the lake. Without annual hydrilla control, reduced boat access could cause severe economic hardships and, eventually, loss of native habitat and a decline in fish production.

How has hydrilla been controlled in the past?

One or two applications of chemicals (herbicides) are usually applied each year. Under normal circumstances, most of the hydrilla is controlled on Lake Toho with one application of chemicals in the winter.

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Why are changes being made to hydrilla control on Lake Toho this year?

In the past five years, Lake Toho has become the most important breeding area in all of Florida for the (Everglades) snail kite, which is one of the most endangered birds in Florida today. These birds have started to feed on large, nonnative apple snails that invaded the lake in 2005. These large snails the birds depend on eat hydrilla, among other plants, and the snail kites are able to capture them while they feed and breathe near the water's surface in the tops of hydrilla plants. Removing hydrilla from areas where kites are nesting makes it harder for the birds to capture snails and lowers the number of young birds that kites can raise on the lake.

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What changes have been made recently to hydrilla control on Lake Toho to help with the endangered snail kite population?

In the past two years, the FWC and the U.S. Fish and Wildlife Service have changed how hydrilla is controlled on Lake Toho to eliminate impacts to snail kites. This new approach involves letting some hydrilla grow where large numbers of kite nests usually occur and conducting hydrilla control in other areas in the late fall/early winter instead of the spring. This approach was not very successful during the first attempt in the winter of 2008-2009, and too little hydrilla remained around kite nesting areas during the early spring months of 2009.

To ensure that hydrilla would be available near kite nesting areas during 2010, a more conservative hydrilla-control approach was taken in the winter of 2009-2010. However, severe cold weather brought complications, and hydrilla was killed back throughout the lake, including the important kite nesting areas.

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What changes will occur during the winter of 2010-2011?

Because of the critical need for snail kites to raise more offspring next year and the unexpected large losses of hydrilla in the past two years, the FWC and the U.S. Fish and Wildlife Service are taking a very cautious approach to controlling hydrilla in the winter of 2010-2011. To ensure that kites will have hydrilla during the early nesting season of 2011, hydrilla will be controlled only in areas of the lake where water must flow freely for flood-control purposes, where it restricts boat access at public boat ramps, and where the majority of navigation is likely to occur.

This may result in a substantial loss of open-water areas in the northern portion of the lake, with navigation possibly restricted to several wide boat trails by mid-summer 2011. The majority of open-water areas will likely occur in the middle and southern portions of the lake. Additional chemicals may be applied in the spring and summer of 2011 to maintain flood-control channels, boat ramp access and navigation trails.

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Will the change in management techniques for hydrilla impact the economy of the Lake Toho area?

The increase in hydrilla on the lake is expected to reduce the areas usable to boaters by summer 2011. Some have expressed concerns that anglers and fishing tournament organizers may choose to go to other lakes in the area. We are working diligently with the local community to maintain lake access and to provide safe navigation so this won't happen. The FWC and the USFWS are working with local business owners and anglers to address many of these concerns. We will continue to assess the network of recreational and navigational channels and re-treat the hydrilla as needed to ensure good access and where possible, actually increase fishing success on the lake. The agencies are committed to address local community concerns, while ensuring we successfully increase the number of young snail kites raised on the lake, which is so critical to the endangered population at this time.

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FWC Facts:
Florida's largest estuary, Tampa Bay, covers 440 square miles and has more than 300 species of inshore fish.

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