Central A/C Draining Causing Stagnant Water - Dry Well?
We see similar things like this quite often.
If the pipe is not overflowing just becoming stagnant.
Get some “summit mosquito dunks” break them in 1/2 and drop a 1/2 in every month. These are fish safe and won’t hurt plants or other animals but will eliminate the mosquitoes by killing the larva.
Depending on where you live 3 or 4 tablets will last a year (not needed in the winter months). This is safer than dropping chlorine tablets in there that may harm other critters and plants.