The invention described herein is that of an outdoor drain filter useful for maintaining the operability of an outdoor drain despite the accumulation of debris that would otherwise obstruct the outdoor drain, resulting in flood prevention of surrounding areas. The outdoor drain filter of the present invention is placed above and around an existing outdoor drain or may be integral with a drain cover or drain reservoir. The outdoor drain filter comprises upper and side filtration means allowing the free flow of water therethrough. The outdoor drain filter further comprises a diverter comprising at least one air vent and at least one lateral pipe that defines a maximum water level to which water will accumulate around the outdoor drain before being diverted into the drain through the diverter. The outdoor drain filter may a manufactured unit or of modular construction.