A water treatment system for a water reservoir comprises a collection box; a rotary drum filter arranged to receive gravity flow from the collection box through a receiving line; a primary bio-filter; a secondary bio-filter; one or more connecting lines originating at the rotary drum filter and comprising at least a first outlet line connected to the primary bio-filter and a second outlet line connected to the secondary bio-filter, the second outlet line comprising a pump; and a return line originating at the primary bio-filter and terminating at the water reservoir. The collection box has a bottom and sides defining an interior volume, and comprises a first water intake having a first riser; a second water intake having a second riser; and a third water intake having a third riser, each riser being disposed inside the interior volume and extend upwardly from the bottom of the collection box.