Wallagoot Lake is a coastal lagoon and intermittently opening estuary set within the scenic Bournda National Park on the Far South Coast of New South Wales, between Tathra and Merimbula. It is a wave-dominated estuary, meaning the ocean reinforces a sand berm at its entrance, which often leads to the lake being closed off from the Tasman Sea for extended periods. Historically, the average closure period is about 15 years, with the entrance last being mechanically opened in 2016 and naturally opening in some years. The lake is fed primarily by Moncks Creek, which has no substantial flow. Despite being sheltered, the lake is surprisingly deep, reaching a maximum depth of approximately 11 metres in places, which is notably deeper than nearby Merimbula Lake. This depth contributes to a unique stratification process where cooler winter temperatures cause the water to "turn over," replenishing oxygen in the deeper sections. The lake's aquatic environment supports a huge diversity of marine life, making it a popular destination for fishing, boating, waterskiing, and birdwatching, with threatened species like the little tern and fairy tern nesting on its foreshores.