Dolphins are around the Northland coastline in huge numbers this summer, but the Department of Conservation is asking anyone taking to the water in the Bay of Island this summer to follow a few basic rules when it comes to interacting with dolphins.

Marine mammal ranger Elke Reufels said seeing bottlenose dolphins was a highlight of many visits to the Bay, but their numbers had been falling in recent years.

It was not clear what was causing the decline so it was important to look after them and avoid putting them under any extra stress.

Approaching dolphins for a closer look was fine but boats had to come in slowly, at no-wake speed, from behind.

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"Please never drive through a pod or cut them off. Also, if it looks like the dolphins don't want to play, please leave them be," she said.

The number of boats with 300m of dolphins was limited to three at any one time. Dolphin encounters should be kept short and sweet, no more than 10 minutes, so everyone had a chance to see them.

Swimming with dolphin pods was not permitted if they had calves (baby dolphins, under 1m in length).

Ms Reufels said dolphins needed a break during the day so should be left alone between 11.30am and 1pm.

"The dolphins need some time out from people and boats, especially during the holidays, so they can just concentrate on looking for their dinner, having a rest and the mums can look after their babies."