For a single piece of infrastructure, Marina Barrage does a remarkable number of things. It holds back the ocean, offering low-lying areas flood protection during storms and a hedge against sea-level rise. It stores fresh water from a massive catchment zone, helping the city-state wean itself off water imports from Malaysia. And on a crowded island of 6 million people, the lawn and the reservoir itself have created some much needed recreational space. It’s a popular place to run, bike, sail boats, and take wedding photos.