Pärnu Bay (Estonian: Pärnu laht) is a bay in the northeastern part of the Gulf of Livonia, Estonia. It has an area of 411 km². The maximum depth in the mouth of the bay is 12 m. The banks are low-lying, sandy in some places. The salinity of the water in the bay is 0-0,8 ppm in the spring and up to 5.5 ppm in autumn. There are several rivers flowing into the gulf, the largest is a River Pärnu. The bay is also Estonia's most important coastal fishing area.