Each year, godwits will embark on the longest non-stop migration of any bird in the world, flying from this site to the Yellow Sea in China, then to Alaska, and returning across the Pacific, direct, to New Zealand.

At the outflow of the intensive dairy farmland of the vast Hauraki Plains, the Firth is among the most modified marine environments in New Zealand, with high turbidity, nutrient loads, pollution and very low levels of oxygen, particularly near the sea floor. It was once carpeted with 500 square kilometres of mussel beds that filtered the outflow of kahikatea swampland, but the kahikatea was felled, the swamps drained and the mussels dredged up by 1960. By then, the sedimentation in the Firth was too thick for mussels to re-establish.