English: Sediment swirled in the shallow water of Lagoa dos Patos in mid-December 2021. The tan stains are created from a combination of a shallow, muddy bottom, heavy inflow from rivers during the wet season, and the action of wind on the surface of the lagoon. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image of this stunning Brazilian ecosystem on December 20, which was the last day of spring and several weeks into the start of the region’s wet season. Measuring about 155 miles (250 km) long and covering about 4,000 square miles (10,360 sq. km), Lagoa dos Patos is the world’s largest choked lagoon. This type of lagoon has only a narrow channel opening to the sea, which significantly obstructs tides from entering the lagoon and also makes mixing of saline ocean waters and inland freshwater. Rather than being open to the Atlantic Ocean, fresh water pours into the lagoon from rivers in the northwest section. This means most of the lagoon’s waters are fresh or just barely saline. However, in the south near a small inlet that communicates with the Atlantic Ocean, the waters are more saline, creating a microtidal estuary. The salinity of the lagoon’s waters varies in this small estuary, based on both the inflow of fresh river water (highest in the wet season) and the inflow of ocean water (driven by tides and wind).