Sorry but that sounds like a horrible idea. You don't say what kind of filters you're using, if you're just using in line rv filters those are mostly just for taste when you encounter well water in certain rv parks. If you're trying to use actual hiking style filters with very small micron filters they require a lot of effort to push the water through (try pumping 20 nalgene bottles through a katadyn filter and you'll get a workout believe me). Depending on water in the lake, how still it is, and what kind of organisms there are there can be a whole host of unwanted things in there. Things like giardia, cryptosporidia, ecoli, salmonella, cholera, hepatitis a, nora virus, and even polio. Depending on how big any of these organisms are in their growth they can still get through a micron filter. When I used to hike and found still water I'd filter it into one bottle designated for unsure water quality, then boil it for 10 minutes, and then put it in a clean water bottle, and on top of that if I was still unsure I'd use iodine. Based on what limited info you gave I'm going to say that what your doing sounds very dangerous and that you've likely contaminated your entire water lines if you're going through your water hookup, or if pumping into your fresh tanks. There is a professional lake water filtration system that can be installed by a qualified plumber, but it's going to cost a lot more than a sump pump and some filters.