I always was told they were "canals" not ditches. Most of the ones originally dug do run to the bay. But they do need to stop developments from using them for storm drainage. From what I can tell they have been making new developments build retention ponds that can be managed by SWMC using several different methods including fish that eat the larvae. Alot of drainage problems in some of the places around here that use them (mosquito canals) for that run into problems because they depend on the tides in the bay to be able to drain water away properly (or in a homeowners point of view..."in a timely manner so my house doesnt flood"). And you can bet that alot of the "poisons" you find in them are from yard runoff not put there by SWMC. I can remember one flood event several years ago that completely blocked 98 near/including 393 to Publix that lasted for several hours,stranding alot of people. I chose to stop at Los Rancheros,have a margarita, and check the tide times. Sure enough about 20 minutes after low tide you could see the water rushing north to the bay.