The Blue Flag is an international environmental award given annually to beaches and marinas. The Blue Flag recognizes the beach or marina's efforts in environmental and sustainability management, safety, water quality, awareness and education, and waste prevention and sorting. They must meet various criteria in doing so.
MarinaPark Bad Nederrijn has also had this award for years. About 130 marinas in the Netherlands are recognized with the Blue Flag.
The purpose of the Blue Flag program is to get governments, entrepreneurs and recreationists permanently involved in caring for clean and safe water, beautiful nature and a healthy environment. Being allowed to fly the Blue Flag is recognition of the efforts made by the beach municipality or marina manager in this area. For the tourist, the Blue Flag is the international recognition and quality symbol for clean beaches with good water quality, safe and clean marinas.
More info on the Blue Flag can be found here.