There's a storm moving in a slow drama across the horizon. Then, it happens: a juvenile humpback whale throws its bulky body out of the water. The watchers point, the crew calls to the skipper, the catamaran turns toward the whitewater. The chase is on.

The northern migration, when whales from the south travel to warmer waters along the east coast of Australia, has begun again. Around 30,000 whales, mostly humpbacks, will travel past Port Stephens as the season peaks around the end of June.

Frank Future, the owner and skipper of Imagine Cruises, takes cohorts of tourists and photographers out beyond the heads to see the environmental marvel.

When Mr Futures arrived in Port Stephens in the 90s, things were different. Only around 300 whales at that time migrated along the coast and the Port Stephens tourism economy, which Mr Futures estimates to be worth around $530 million annually, was mostly a summer affair.

"When I first came to Port Stephens, there was no whale watching," he said. "Although tourism was always a significant part of our economy, it went from October through to Easter. But in the winter it virtually stopped."

Nowadays, whale watching injects millions of dollars each year into the local visitor economy and has made tourism a year-round enterprise for the town.

Being on the water is like falling out of time. The lighthouse on a spit of land poking out into the sea is the only hint of industrialised life. The water breaks at the feet of enigmatic islands and low clouds hang around their peaks. There is a feeling of wilderness here; an ancient place.

Before the arrival of colonial settlers, the water and islands provided for the Worimi people who built canoes from bark stripped from local trees and made campsites on the islands.

The volcanic landscape is as much an attraction for whale watchers as the great and gentle leviathans below the surface.

"It keeps me going," Mr Futures said with a laugh. "Every day is different. Even on a rainy day like today.

You dont know what is going to happen.

But despite all the natural beauty, there is something disturbing in the awe. As the catamaran makes her way toward the migration ground, pieces of plastic and debris float by in all directions.

On Yacaaba Headland, the sister jut of land alongside Tomaree, a shipping container lies in ruins on the beach.

A container ship called YM Efficiency had run into rough seas the previous week and lost 83 containers overboard. Debris had littered the coast - plastics, nappies and toilet-paper packaging.

Residents had started a clean-up operation over the weekend, and the Australian Maritime Safety Authority (AMSA) and NSW Roads and Maritime Service (RMS) had stepped in to lead the recovery efforts. Mr Futures was concerned the extent of the damage could still be unknown.

Several of the 83 lost containers had sunk, he said. Aside from the danger of colliding with a submerged container, there was no telling what effect the contents would have when they eventually broke down.

"I don't think it is going to have a lasting effect, but how long it takes to see the full effect is anyone's guess at this point, Mr Futures said. We have seen one container. But what happens to the rest of the containers as they decompose is anyone's guess.

The amount of plastic in the water worried the skipper. In the weeks before heading out on June 6, his boat had taken on a piece of plastic that destroyed an engine and temporarily put the catamaran out of action.

In his time as a sailor, Mr Futures had heard reports from other parts of the world of autopsied whales found with kilograms of plastics inside them and turtles killed after eating plastic, mistaking it for jellyfish.

"They are long-living reptiles," Mr Futures said. "Some turtles live more than 100 years, and for an animal to live that long and then die because of plastic.

"It is our responsibility; if we make it or use it, surely we have a responsibility to keep it out of the environment."

As the steady rain comes and goes, a pair of humpback whales come up for air.

They spend a few minutes on the surface, breathing, slapping the water. On the deck, the watchers are in awe. They almost forget the cold and the rain tapping on their spray jackets.

A dorsal fin pokes out of the rolling swell, like the tip of an enormous iceberg; there is a hint of something massive beneath. A broad tail follows and slips silently into the deep.

Then, just as quickly as they arrived, the whales are gone. The water is quiet again. The boat waits.

Before the cold can seep in, the water breaks on the horizon as a young whale hurls itself out of the churn. Camera lenses go up, the boat turns, and the chase is on again.

- Send your whale watching photos to news@theherald.com.au

- Contact: simon.mccarthy@fairfaxmedia.com.au