They can be a real problem at times, all around the lake system. I never see them at the ocean beach in Loch Sport. If you're looking to holiday or buy in the area, look for an elevated (ie on stilts) or two-storey house with a decent sized balcony. The mozzies are much less of an issue once you get off ground level, and you will appreciate being able to sit outside on your balcony without being bitten.
Mosquitoes are mostly a problem around paynesville, newlands arm and eagle point. They are mainly present during summer and after rainfall. Good mozzie protection should work, I've heard bushman's mozzie repellent is the best which is available from the Eagle Point Store!