Aquatic life is the engine of ecosystems and economies. In environments ranging from freshwater through marine, this biodiversity underpins the health, culture, opportunities, and economic wellbeing of the Nation -- from local communities to the entire country. The ability to evaluate the status, trends, and future projections of nature is key to maintaining national prosperity, and this requires timely and trusted information about the condition of aquatic biodiversity on a vast scale. With one of the largest Exclusive Economic Zones in the world and extensive estuaries, lakes, rivers and streams, it is a grand challenge for the United States to explore, monitor, and understand aquatic life.