Discouraging Frivolous Lawsuits Act This bill amends the Federal Water Pollution Control Act (commonly known as the Clean Water Act) to revise requirements concerning citizen suits. Litigation costs (including reasonable attorney and expert witness fees) must be awarded to the prevailing party, thus the bill removes a court's discretion to award the fees. A prevailing party is defined as the party that prevails on more than half of the claims at issue. The bill repeals the authority of the Environmental Protection Agency (EPA) to deny or restrict the use of any area as a disposal site for dredged or fill material when the discharge of those materials would have an unacceptable adverse effect on municipal water supplies, shellfish beds and fishery areas, wildlife, or recreational areas. Current law requires compensatory mitigation to replace the loss of aquatic resource functions in a watershed when a permit to discharge dredged or fill materials into navigable waters has unavoidable impacts on aquatic resources. This bill prohibits government entities from carrying out compensatory mitigation in excess of existing regulatory requirements.