I have a lake that is about 8 acres in size. It became infested with coon tail about 10 years ago. Now it covers about 2/3rds of the lake. My grandfather had this lake built in 1954. Had bulldozers dig out about 2 acres of ground to build a dam across a creek that runs through our property.The dam is over 100yds long with a spillway that empties back into the creek behind the dam. The dugout part of this lake is about 20 feet deep when full.Mid lake runs about 6 to 8 feet deep.The main forage food is bluegill and other perch species. Before the coontail got in the lake we were catching bass up to 9lbs with lots of 4 an d 5 pounders. You could fish anywhere on the lake with t rigs, jigs,crankbaits or whatever and catch fish. Now I can only fish about 2 acres of the lake where the coontail does not grow.The growth is so thick the only thing that lives among it is the blue gill. What is the best way to rid of the coon tail in my lake. I know chemicals for that size lake will be expensive.

Rated EXCELLENT: Herbcide

Diquat
Endothall
Fluridone

Agreed.

Flumioxazin is also very effective with full effect in days, but the coontail will regrow in a few weeks.
Diquat full effect in days to a week or so, probably a little longer control than flumioxazin, so long as the water is not muddy (diquat binds to suspended clay becoming ineffective). I imagine your water is very clear though so no worries.
Endothall (dipotassium salt / aquathol) also works quickly, days to a week or so for full effect. I'd avoid hydrothol (dimethylalkylamine salt) because the dose rate necessary to kill weeds is close to lethal concentrations for fish.

These three kill weeds fast so do not treat more than 1/3 to 1/4 of the pond at one time or you will cause an oxygen depletion from too much plant decomposition at one time and you will likely kill your fish (again, not from chemical toxicity, but from oxygen depletion from decomposing plants). Wait two weeks between treatments to give dead plants time to decompose before hitting the next section. You will probably see regrowth in a few weeks to a month or so.

Fluridone is a very slow systemic herbicide. It takes as long as 3 months for full effect and it needs at least one month of maintaining the correct concentration for full effect (meaning no water in or out during the treatment period or the chemical will get diluted and may not work as well). The upside is that you treat the whole pond at one time with low risk of oxygen problems (the plants slowly die over time) and when the plants are dead, they are dead to the roots and gone for months to years.

All chemicals work better when applied earlier in the year but they will still work right now. You just have to be extremely careful with fast-acting contact herbicides because they can kill a bunch of weeds quick, causing oxygen problems and fish kills.

For long-term maintenance, grass carp can be helpful. It takes about 15 or more per acre to help control coontail (they eat it but don't love it). Grass carp alone will probably not get the current infestation under control for a couple years, if ever; best to use chemicals to knock the weeds back then use grass carp as maintenance. Another problem with grass carp is they tend to be all-or-nothing control measures. It's essentially impossible to predict the perfect number of carp to provide enough vegetation for good fishing (about 20-30% area covered). The carp will either not eat enough, or they eat every blade of grass in the pond. At least with contact herbicides you can be selective on where you kill, with the understanding that it will be something you'll have to do every few months till the end of time. Pick your struggle lol. You'll need a permit from TPWD to stock triploid grass carp.

Aquatic dye can help shade the water and suppress growth deeper than about 3-4 feet. Dyes won't kill weeds but they slow them down. Dye also suppresses beneficial plankton so it's not a perfect approach either.

If you can get the coontail controlled by the end of this year, you can try a light dose of fertilizer when the water gets to about 65 degrees next spring to encourage a plankton bloom. If you can get the bloom established early, it'll gobble up a bunch of nutrients and light that would be going to the weeds. Plankton is the base of the food chain, so it will help your fishery recover as well. You likely now have stunted bluegill and stunted largemouth that will both require culling to get growth ramped back up after the weeds are controlled. Do not add fertilizer to the pond if a bunch of coontail remains, it will only make it worse (coontail absorbs nutrients from the water, not roots). Lots of work, but you can fix it with money, time, and patience.

Scott, nailed it. What an incredibly nice person to write such a thorough reply that is ACCURATE. So, much of what you read is incorrect, by well intenioned people. But, Scotts information and guidance is spot on!

COPPER SULPHATE will work also and should be a lot less expensive plus can be bought at TSC.

Copper Sulfate is slightly less and is also slightly less effective on Coontail.

If you can afford it. Use Flouridone.

Copper Sulfate is less expensive, (about 1/3 the cost). However, you must use about twice as much for control and apply more often than diquat.

If you can afford it. Use Flouridone.