Imagine the old Kopu Bridge as a cycle track: no delays, no road rage, just a quick push across the Waihou River towards Thames.

That just may happen under a cycleway plan, using mangrove-fringed stopbanks which keep the Firth of Thames out of the low-lying Hauraki plains.

Famous for its migratory birds, the seacoast beside the shallow reaches of the Hauraki Gulf draws 50,000 visitors a year.

Backers of the cycleway plan - given fresh impetus by Prime Minister John Key's enthusiasm for a network of tracks across New Zealand - believe they could double the number of tourists and inject $3.6 million into the local economy inside five years if they get their wheels turning.

Across the Waihou, the Hauraki Rail Trail Trust is cranking up its idea to use old rail corridors running from Paeroa to Thames, and from Paeroa through the dramatic Karangahake Gorge to Waihi. The scheme is based on the central Otago rail trail.

Trustee Mike Hayden said a study calculated the T-shaped network could generate $11 million a year.

Part of the income was savings from fewer accidents involving cyclists risking their limbs on the busy, narrow road which twists through the gorge. "One of our goals is safety - to get cyclists off the main roads."

Talks had been held with farmers for access through their land, with railway operator Ontrack and the NZ Transport Agency, which is funding a $32 million new Kopu Bridge.

Cyclists and walkers can use the new bridge but Hayden would like cycle access to the 81-year-old original.

No firm cost exists for the full project, though Hayden expects it would run to millions of dollars. Much of the money would go on time-consuming consents and approvals. But he thinks it fits firmly within the Prime Minister's vision, which has shifted from the initial stretch of concrete from Kaitaia to Bluff to a network of tracks.

Hayden is not a fan of concrete: "We would use a fine gravel on the rail tracks. People don't want to walk on concrete."

Special gates to stop motorcycles and quad bikes would keep track users and farmers happy, he says. "We would want to be a good neighbour."

He says of the trust's agenda: "It's ambitious but it can be done, It seems so obvious and would give small communities a shot in the arm."

Back on the western side of the Hauraki Plains, Bill Brownell, who convenes the Muddy Feet Project - a group comprising those with interests in the lower gulf - is looking for $60,000 to show its "seabird coast" tourism plan will work. One of those he intends to lobby is John Key.

"We were quite blown away when he started talking about a cycleway, because here we have a done a lot of work on the idea."

Brownell, a keen cyclist, imagines the chance to enjoy some of the country's largest flocks of shorebirds - godwits, wrybills, knots, turnstones and oyster catchers - wheeling above shimmering, bleached shell banks from the seat of a cycle could be an irresistible new drawcard.