Mystic River pedestrian/bike bridge would be longest of its kind in Boston region

State officials have unveiled plans for what would be the longest bike and pedestrian bridge in the Boston region: A 780-foot run from the future Wynn Boston Harbor casino resort in Everett to the still-unfolding Assembly Row neighborhood in Somerville.

What amounts to a bridge over the Mystic River would cost around $30 million total—as of now—but it’s not clear who would foot the bill.

As the Globe’s Adam Vaccaro notes, the government agencies involved are not rushing things finance-wise, and the development forces behind Wynn Boston Harbor and Assembly Row are not really offering much besides warm wishes (though Wynn has offered $250,000 for an initial phase of the bridge).

Perhaps it’s because the project’s location and various moving parts make its timetable and design uncertain.

For one thing, it would require a separate walkway over the train tracks to Assembly Square’s Orange Line stop, a project that on its own could add $10 million to the cost. There is also the growth on either would-be end of the expanse—and the very real possibility that an Amazon HQ could factor in to final plans.

It was Assembly Row’s growth and that Orange Line stop, which opened in 2014, that made the idea of a bike-pedestrian bridge alluring in the first place, according to Vaccaro.

There’s also the uncertainty over the future of Wynn Boston Harbor, given the sexual assault allegations against Steve Wynn, the company’s now-former chief executive. The casino-resort is still on pace to open in 2019.

Stay tuned.

• Who will pay for a $23 million footbridge to the Wynn casino? [Globe]
• Somerville’s tallest building has started welcoming its first residents [Curbed Boston]
• Steve Wynn resigns as Wynn Resorts chief—but what’s that mean for Boston? [Curbed Boston]
• Amazon in the Boston area: 6 likely sites for the e-commerce giant [Curbed Boston]