As with most insects, if the 'conditions' are right, they'll breed. So, hypothetically, if you alter the conditions enough, they'll move on.
What you might want to consider is clearing out any vegetation to improve sunlight and airflow. In most cases, warm, dry conditions won't spur breeding in animals that like a natural, lake type-of climate. Beings you're on a lake, this isn't exactly what you want to hear BUT it may help alleviate your problem. You can try by experimenting. Pick an area large enough to have an impact. Clear out the vegetation and trim some trees to let air and sun in, and see what happens. If it works, then you have a 'feel' for what has to be done. You can do a little each time until you get the desired results.
As you've seen, the problem with sprays and foggers is that they're temporary. Check around the neighborhood and introduce yourself to neighbors that have 'cleared' their lots a bit. See if they have a similiar problem. (Now's not the time to be shy!) Other than this, I haven't much else to offer.
FWIW, I had a mold and mildew problem around my home. I removed some bushes, trimmed some trees, and planted low-growing vegetation and I no longer have the problem. I improved the sunlight and airflow and that was enough to rid the 'prime conditions' for that stuff to grow. You should have the same luck. So if there's lots of shade and stagnent air, get some sun and air 'in there' and see if it's enough to change the situation. Again, talk to neighbors that have already cleared, and heck, talk to those who HAVEN'T cleared their lots to hear what they have to say.
My best to ya and hope this helps. When the weather comes around, I'd appreciate a follow-up from ya. Save my e-mail address in your Address Book. I'm betting my suggestion will work.