Piwoslaw's idea is probably the easiest and cheapest option, also possibly the best, but here was my original thought for something like this.
Look at places that sell water pumps, they will have metal filters or strainers, just find one with a really tight strainer grid and be sure the water isn't being pumped at the very bottom where it will pull up sludge and when you are getting started, check the screen often to be sure its not clogged and after awhile if it never needs cleaning then you won't have to check as often.
Here are some examples, I've seen a few of these stocked in the stores but I don't know if they have the full selection.
Puddle Skimmers + Water Pump Strainers | Water Pump Accessories | Water Pumps | Northern Tool + Equipment