A Southern right whale is taking her time swimming up the Northland coastline to the delight of locals who are catching a glimpse of the impressive mammal on its journey, but the public is being urged to follow the whale-watching rules.

The adult female whale hit the headlines when it was spotted lolling about in Mechanics Bay, and could be seen from Tamaki Drive in Auckland earlier this month. Since then it has been seen off Omaha, then lolling in the calm waters of Smugglers Cove at Whangarei Heads last Saturday.

It delighted beachgoers at Sandy Bay on Tuesday and then on Friday the whale was seen by Bland Bay campground manager Tupou Johnstone at Puriri Bay on Whangaruru Harbour.

"It was huge. You knew it wasn't an Orca or a dolphin. It was like a long black log in the water," Mrs Johnstone said.

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She was surprised it was in such shallow water.

"It was swimming at a very slow pace. I could see white on its nose and then it was flipping its tail around." The white is known as a callosities and refers to the rough, calcified skin patches which are like a fingerprint for each whale.

Right whales were named by whalers who identified them as the "right" whale to kill on a hunt because they are slow-moving and are usually near the surface. Southern right whale populations are showing a slow increase since international protection in 1935, with an estimated 3000-4000 in the southern hemisphere.

Whale expert Ingrid Visser of Tutukaka said this was the time of year the right whales were seen off the Northland coastline as they slowly migrated to northern waters during winter.

She said southern right whales used to be seen as far north as the Kermadec Islands and as far south as the subantarctic Auckland Islands.

It was unclear how long the whale would hang around but it looked like it would make it to the Bay of Islands by the weekend. Department of Conservation officials caution whale watchers to remain at a safe distance.

Marine technical advisor Andrew Baxter said the whales could lash out and deserved to be treated with respect. Under the Marine Mammals Protection Act, breaking the rules around marine mammals can lead to a maximum penalty of up to two years' jail or a $100,000 fine.

If you spot the whale Dr Visser wants to know - call 0800 SEE ORCA (0800 733 6722).

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Marine Mammal Rules:

• Ensure you travel no faster than idle or "no wake" speed within 300m of any marine mammal.

• Approach whales and dolphins from behind and to the side. Do not circle them, obstruct their path or cut through any group.

• Keep at least 50m from whales (or 200m from any large whale mother and calf or calves). Swimming with whales is not permitted.

• You may swim with seals and dolphins but not with dolphin pods with very young calves.

• Offences carry penalties of up to six months' imprisonment or fines up to $250,000 and further fines of up to $10,000 for every marine mammal in respect of which offence is committed.