Waituna

A waituna is a freshwater coastal lagoon on a mixed sand and gravel (MSG) beach, formed where a braided river meets a coastline affected by longshore drift.

Both waituna and hapua are rare globally but common in New Zealand, where they are considered ecologically significant as sites of traditional Māori food-gathering as well as for their diversity of fish and bird species.

Both waituna and hapua are fed by small rivers flowing out to an MSG beach, on an eroding wave-dominated coast, with strong longshore drift.

Hapua are long-lived river mouth lagoons, whereas waituna are ephemeral coastal "lakes" that do not persist over geological time.

Hapua persist because the river mouth turns sideways and carves out cliffs on a daily basis, whereas waituna form when gravel creates a barrier that impedes the drainage of freshwater.

[3] Waituna are low in salt, high in water that lies around for a long time, and shallow – typically less than 3 metres (9.8 ft) deep.