Paoay Lake is a lake within the municipality of Paoay, in northwestern Luzon, Philippines. It is the largest lake in the province of Ilocos Norte and one of the largest natural lakes in the area. Historically known as Lago de Nanguyudan, the lake supposedly was the site of a prosperous barangay called San Juan de Sahagún that sank after an earthquake. The fres…Paoay Lake is a lake within the municipality of Paoay, in northwestern Luzon, Philippines. It is the largest lake in the province of Ilocos Norte and one of the largest natural lakes in the area. Historically known as Lago de Nanguyudan, the lake supposedly was the site of a prosperous barangay called San Juan de Sahagún that sank after an earthquake. The freshwater lake and its 1-kilometre surroundings was declared a national park in 1969 by virtue of Republic Act 5631. In 1978, through Presidential Decree 1554, the park was reduced to an area of 340 hectares concentrated on the lake itself around its highest water level.