A portable cofferdam system for isolating a working area from water such as a culvert. The portable cofferdam system generally includes a first sidewall and a second sidewall each having an interior side, an exterior side, an upper edge, a lower edge and a rear edge. A middle wall is connected to the sidewalls opposite of the rear edges of the sidewalls forming a substantially U-shaped structure. An opening formed between the rear edges of the first sidewall and the second sidewall to allow for positioning about or near the inlet of an object or area to be kept dry such as the inlet of a culvert.