Standing in downtown Anchorage one can gaze across Cook Inlet and clearly see Alaska's Matanuska-Susitna Valley just two miles away. But despite its proximity and the waterway's narrowness, getting there takes at least an hour. That's because no one's built a bridge across it.

Wedged between a federal military installation, the Pacific Ocean to the west, the Chugach Mountains to the east, and the Chugach National Forest to the south, Anchorage is essentially out of developable land but remains the state's commercial and financial hub. People and businesses have been moving further north to the Matanuska-Susitna Borough, where land and houses are less expensive. Though the region contains 54% of the state's population, it's connected by one road, the Glenn Highway. Not surprisingly, congestion is a problem.

A crossing was first proposed by railroad engineers in 1923, a few years after Anchorage was established, to shorten the distance between Anchorage and Fairbanks, an active mining town 358 miles to the north. As Cook Inlet evolved into the state's main shipping route and became a focal point for oil and gas exploration, the crossing had been proposed a half-dozen times since then. In 2003, after years of planning and studies, the Alaska Legislature formed the Knik Arm Bridge and Toll Authority to enable continuing economic development and provide an alternate evacuation route.

Our main concern was a beluga whale subspecies that uses the inlet to get to and from breeding areas. So the first thing we did was ask state and federal regulatory agencies — in particular the National Marine Fisheries Service (NMFS) — to become cooperating organizations.

“We wanted to identify all areas of concern, but specifically we wanted to know what considerations the Cook Inlet belugas needed since the species was listed as ‘depleted' under the Marine Mammal Protection Act in 2000,” says Authority Executive Director Andrew Niemiec. The service was concerned that assessing potential impact would be virtually impossible because there wasn't enough information on how the whales use the inlet.

In June 2004, we kicked off a six-month direct observation program around the Port of Anchorage that was expanded to 12 months at the service's request. We learned how the whales react to in-water structures, their seasonal patterns, and what prey species they prefer; and mapped high-value/high-sensitivity habitat such as summer feeding grounds within the inlet.

Because other whale species have shown some aversion to passive in-water structures, the service was also concerned that belugas may hesitate to swim under the bridge, impeding their travel to and from feeding grounds. Not only do they tolerate them, they pass back and forth under 14 other bridges in Southcentral Alaska and at least 15 additional bridges worldwide without harm. Our finding reassured all parties that the species habituates to a variety of circumstances and was unlikely to abandon the inlet after a bridge was built.

We also discovered patterns of use. Beluga numbers are greatest from August through October, when the whales come in on the flood tide and leave on the ebb tide. And while they feed primarily on salmon during spring and summer, they're opportunistic feeders that eat whatever is available —from squid to sole and cod to clams.

This baseline work allowed us to produce a Final Environmental Impact Statement in 2007. A year later, the whale's status was changed from “depleted” to “endangered.”

In general Alaska's beluga populations are healthy, but legal subsistence hunting had halved Cook Inlet's numbers. Between 1994 and 1998, the population fell from 653 to 347. Even though hunting's been regulated since 1999, their numbers hadn't rebounded. Having established Cook Inlet's stock as a distinct genetic population, the service recategorized the subspecies under the Endangered Species Act.