An adventurous seal has made an epic 75 kilometre journey through the canals of the Waikato before running out of steam outside a farm shed.

But the frisky female, named Cedrica, still had enough pounce to chase a police officer around a patrol car before being swaddled up by the Department of Conservation.

It is not known when the seal's journey began but she was discovered lying high and dry on the edge of Horrell Rd near Morrinsville on Sunday morning.

A passerby noticed something unusual on the roadside and called police who made the discovery, Morrinsville police Sergeant Vic Sneddon said.

"We have images of her chasing one of our staff around a patrol car so while it may have had problems adjusting its internal GPS, she still had plenty of life left in her.

"But in terms of how she came to be there in the first place, its lips were definitely sealed."

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It was not known exactly when the seal began its journey from the Firth of Thames but Department of Conservation ranger Garry Hickman believed it used the Piako River to navigate in and out of the canals during heavy rain through the Hauraki Plains.

"They come up the rivers, sometimes there can be one or two. They are chasing trout, mullet, koi carp, so it's not hard for them to get a feed.

"They have to chase the fish - they are opportunists."

Hickman arrived at Horrell Rd to find the docile seal napping in the shade about 15 metres from the road.

"It looks like it had been out of the water for quite a while as it was pretty dry, the nearest drain would of been about 100 metres away."

He said the seal - measuring about 1.5metre long - made a move, clambering through a farm fence into a paddock.

"You can walk up to a seal and it looks really docile but they can react like lightning."

With the help of police officers, the trio approached the seal from different directions, boxing it in.

"I threw a net over it while it was looking the other way. It hissed and snarled and bared it's teeth as they do."

The seal was then put in a polypropylene box and driven to Tapu where Hickman released it back into the sea from the beach.

"When I let the bag go on the rocks she popped her head up, looked at me, and swam back into the ocean."

DOC received a call about a seal on nearby No.8 road the day before and it was likely the same seal.

"They are a common sight - you get them in Okoroire, Te Aroha, even Lichfield, occasionally we get big ones, this was a medium size.

"In this case it had been on the road and if someone hit it at 100km they could have been off the road and dead, so it was the smart thing to do."

Numbers of seals coming ashore were increasing, Hickman said. He'd received the highest number of callouts to rescue seals this winter.

"The numbers are increasing and we are now seeing seals in different places where they haven't been found in a long time."

Seals had recently been found in the streets of Raglan and roadsides of Kawhia, he said.

"They are coming a long way downstream and they are here to stay."

If people come across a seal they should avoid any contact, keep dogs away and contact Department of Conservation.

"They are like any other animal if they consider you a threat they are going to do something about it - they also carry some pretty nasty diseases, such as tuberculous."