![OKEECHOBEE -- The main water intake for the Okeechobee Utility Authority is west of the "Lock 7" pier. The secondary water intake is in the Rim Canal. [Art courtesy OUA]](/uploads/original/20251117-131241-f02-OUA intake map JPG.jpg)
Editor’s note: This is the seventh in a series of articles examining the use of chemical herbicides to control invasive aquatic plant growth in Lake Okeechobee.
Okeechobee Utility Authority (OUA) customers have a personal interest in the use of chemical herbicides on plants in Lake Okeechobee. The lake is OUA’s primary source of potable water. The main water intake is in Lake Okeechobee, west of the “Lock 7” pier.
What happens if there are invasive plants near the OUA water intake?
Zachary Fletcher, of Florida Fish and Wildlife Conservation Commission (FWC), explained: “When invasive plant management is required within the lakeside potable water intake area, FWC staff request the Okeechobee Utility Authority temporarily draws water from their secondary intake location as an additional precautionary measure. Crews are directed to remain 500 feet from the lakeside intake when management is not required, and crew locations are monitored by GPS in real time.”
Is 500 feet of buffer sufficient to protect OUA water customers? The answer depends on which herbicides are used and the concentration used.
According to the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Center for Aquatic and Invasive Plants website FWC is the lead agency for aquatic plant management in Florida. “FWC issues permits and contracts for the control of aquatic plants, much of which is achieved using EPA and FDACS-registered herbicides. FWC authorizes the use of registered herbicides by state contractors on work plans for each public water body,” the website states.
Fletcher stated herbicides used to treat invasive aquatic plants on Lake Okeechobee in 2025 include:
• Imazapyr: Used to control Cyperus blepharoleptos (Cuban club-rush), Ludwigia grandiflora|hexapetala (large flower Primrose Willow), Luziola subintegra (Tropical American watergrass), Panicum repens (torpedograss);
• Sethoxydim: Used to control torpedograss;
• Diquat: Used to control Cuban club-rush, Eichhornia (water hyacinth) and Pistia (water lettuce), Scleria lacustris (Wright’s nutrush);
• Glyphosate: Used to control Cuban club-rush, Imperata cylindrica (cogon grass), large flower primrose willow, Tropical American watergrass;
• Flumioxazin: Used to control water hyacinth, water lettuce, Ipomoea sp;
• ProcellaCOR: Used to control water hyacinth and water lettuce;
• Triclopyr: Used to control Schinus terebinthifolius.
“Penoxsulam, 2-4 D, and Imazamox are also herbicides that work on water hyacinth and could be utilized,” Fletcher added.
The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Center for Aquatic and Invasive Plants website states the U.S. Environmental Protection Agency (EPA) and the Florida Department of Agriculture and Consumer Services (FDACS) determine which herbicide active ingredients are registered for use in aquatic sites in Florida.
FDACS is the state agency designated to regulate pesticides used in Florida, and the Florida Pesticide Law (Chapter 487, Florida Statutes) is used for this purpose. The Florida Department of Environmental Protection (FDEP) is responsible for implementing EPA regulations for chemicals applied to waters within Florida.
UF/IFAS Center for Aquatic and Invasive Plants website “Herbicides Registered for Use in Florida Waters” includes the following information on the herbicides used by FWC spray vendors on Lake Okeechobee.
IFAS lists Imazapyr as “Low toxicity to fish, non-toxic to waterfowl.”
Warnings include: “Do not apply within 1 mile of active irrigation water intake.
“Do not apply within 1/2 mile (2,640 feet) upstream of a functioning potable water intake.
“Do not apply within 1/2 mile of an active potable water intake in a standing body of water. Applications within 1/2 mile of potable water intake can be made if the intake is shut down for a minimum of 48 hours.”
Half-life in water is about 2 days.
The IFAS website warns “Do not apply within 500 feet of an irrigation intake for crop growing area.”
It also warns, “Do not use water in the immediate area where TIGR herbicide is applied for drinking for 30 days after application or until analytical monitoring has verified less than 1 part per billion (ppb) in water.”
The IFAS website warns: “Avoid applications within newly installed revegetation sites.”
The website advises diquat has “slight to moderate toxicity to fish.” It also notes the herbicide is “moderately toxic to birds.”
It advises the applicator “coordinate with water facility manager for applications within 1,600 feet of an active potable water intake,” and to use “rate dependent setbacks of 350-1,600 feet from functioning potable water intake.”
Half-life of the herbicide in water is 1-2 days. Soil dissipation half-life may exceed 3 years.
The site warns: “Avoid mixing with or applying to turbid waters; binds tightly to clay and organic particles.”
Glyphosate has been the source of controversy for years, with some countries banning its use over concerns about danger to human health. While the herbicide has not been banned in the U.S., some counties and cities have local bans. In 2019, Miami banned use of glyphosate by the county employees and contractors. Key West, Fort Myers, Miami Beach and Satellite Beach have similar ordinances.
The IFAS site warns: “Do not apply within ½ mile upstream of a functioning potable water intake or within ½ mile of a functioning potable water intake in static water.” (One-half mile equals 2,640 feet.)
The website adds that applications can be made if the intake is shut down for 48 hours or an approved water analysis indicates the glyphosate concentration is below 0.7 parts per million (ppm).
Half-life of the herbicide in ponds is approximately 12-60 days.
IFAS warns: “Avoid application in winds greater than 10 mph.”
Flumioxazin is listed as “moderately toxic to fish.”
There are no potable water restrictions.
The website notes this herbicide has a short half-life I water, depending on season, water depth and especially pH. The half-life in water with low pH (6.0-6.2) is approximately 39 hours. Half-life in medium pH (7.0-7.2) is approximately 18.6 hours. Half-life in high pH (>8.5) is approximately 1.7 hours.
Half-life in soil is approximately 45 days.
ProCellaCOR is not on the UF/IFAS list of Herbicides Registered for Use in Florida Waters. ProCellaCOR's
The IFAS website states this herbicide is “practically non-toxic to fish” and is “non-toxic to waterfowl.”
Recommended setback from potable water intake depend on the size and rate of application.
The herbicide has a half life of 2.5 days in shallow water/summer to 14 days deep water/winter.
Half-life in soil is about 45 days.
There are no restrictions on the use of Penoxsulum on potable water. The website states: “Do not apply to waters used for food crop irrigation until concentration drops below 1 ppb. Avoid applications within or adjacent to newly planted aquatic revegetation sites.”
Average half-life in Florida waters is 2 to 4 weeks. Dark or tannic stained waters may decrease sunlight and prolong half-life.
Warnings about 2,4-D include: “Do not irrigate with treated water, if applied within 600 feet of functioning water intake; until 7 days after application within 600 feet of irrigation water intake, or; an approved assay of water taken 3 days after application demonstrates a 2,4D concentration of 0.1ppm or less.”
The site also warns: “Do not apply within 600 feet of a functioning potable water intake for floating plant control. Coordinate applications with facility water operators.”
Half-life of 2,4-D in water is 7-10 days.
Warnings also include: “Highly volatile -- do not apply in winds greater than 5 mph.”
The IFAS website states this herbicide is “practically non-toxic” to fish and waterfowl.
No water restrictions are required if applications are ¼ mile or more (1,320 feet) or more from potable water intake. “Shut down water intake if application exceeds 50 ppb within ¼ mile of water intake,” the website advises.
In gathering information for this article, on Nov. 17 the newspaper reached out to FWC with the following questions:
How did FWC determine that 500 feet was a safe distance?
The article will be updated on the LakeO.com website as more information becomes available.
On Dec. 2. Zachary Fletcher of FWC responded to the questions: "Potable intake restrictions and application setbacks are specified by individual product labels. FWC staff and contractors follow the label directions of any product used, which include these directions if required for a given product."
He did not provide the requested information about how close to the water intake the herbicides were sprayed over the past year.
NOTE: This is a continuing series. We welcome feedback from the public. Email kelsken@iniusa.org to share your views and photos.
Other stories in this series include:
Residents who live on canals oppose herbicide spraying
FWC uses GPS to track spray contractors
Invasive plants disrupt Florida’s food chain
Herbicides sometimes hit native plants
