I use this with moderate success. I think my limited success is the nature of the creek constantly cycling out water.
In the US they can be bought as mosquito bits/dunks https://summitchemical.com/products/mosquito-bits/
It is important to note this is not a poison. It is a naturally occurring bacteria that is harmless to the food chain (Bacillus thuringiensis). That is important to me and, I think, a lot of others.
https://www.youtube.com/watch?v=tPIO86jTrQQ&list=RDtPIO86jTrQQ&start_radio=1