Hornsea Mere is the largest freshwater lake in Yorkshire, England, and lies to the west of Hornsea in the East Riding.
It covers an area of 467 acres (1.89 km2), is 2 miles (3.2 km) long, 0.75 miles (1.2 km) at its widest point and 12 feet (3.7 m) at its deepest.
Hornsea Mere is a centre for bird-watching and a tourist attraction offering rowing, sailing, boat trips and fishing. It is a designated Site of Special Scientific Interest and a Special Protection Area for birds; it accommodates many species throughout the year, and is of international importance for a migratory population of gadwall. It's shallowness results in a diverse range of swamp and fen plants.
It was featured in the BBC television programme the Seven Natural Wonders.
Hornsea Mere is owned by Wassand Hall, situated to the west of the mere, and was purchased by the Hall's estate for £50 in the 16th century.