Lake Grassmere / Kapara Te Hau is a New Zealand waituna-type lagoon in the northeastern South Island, close to Cook Strait.

Covering an area of 17 square kilometres (6.6 sq mi), it has no natural inflow and is prone to strong warm winds.

The climate, with a low average rainfall of 585 millimetres (23.0 in) and prevailing strong and dry north-westerly winds, provides Lake Grassmere with the suitable conditions required for natural economic salt production.

Scouts from Te Rauparaha's party found the locality apparently uninhabited and the canoes were driven ashore.

Until the 1940s Grassmere's bed was a mud bath in winter and a dustbowl in summer, with the occasional natural deposit of salt.

The salt industry began in 1943 and now occupies one-third of the suitable lake area of 15 square kilometres (3,800 acres).

In the mid 1960s harvests were carried out with a new pattern of crystallising ponds which have special provision for draining off rainwater before it has had time to mix with the brine concentrate.

By 1970 the harvest had increased to almost 52,000 tonnes, but this could not match demand, which had grown with industrial development (especially from freezing works and pulp and paper mills).

A large range of salts with slightly different chemical compositions, grain sizes and shapes are produced at Lake Grassmere.