Big Lagoon, sometimes known as Te Whanganui (both unofficial) is a lagoon beside Cloudy Bay in Marlborough, New Zealand.

There used to be a canal known as Ōrua or previously Morgan Creek which went from Ōpawa River to Big Lagoon.

[3] Big Lagoon was previously a wildlife refuge, but this has been lifted and people are now permitted to hunt over the lagoon.

[4] Big Lagoon has beds of Ruppia, Chara and Nitella.

This means that Big Lagoon occasionally experiences strong earthquakes, which may cause liquefaction.