Geogrids have been used in hundreds of reinforced slopes and wall projects in the world. The Keppel-Sentosa Road Link project in Singapore was the first time where geogrids were used to build a 1 lm high reinforced slope totally situated under the sea level. The slope, built with gravel and stones reinforced with HDPE mono-oriented geogrids, was aimed to provide easy access to water level in case of any need. To serve such a need effectively, the slope had to be rather steep. Therefore it was decided to reinforce the slope with HDPE geogrids, which are resistant to the aggressive environment of the sea. The paper describes the design principles used for this challenging project and the construction method, which involved the co-ordinated work of the contractor and of many scuba divers.