Glacier Bay stretches more than 60 miles from its mouth at Icy Strait to the base of the tidewater glaciers at its northern end. Quite impressive, particularly when you consider that it didn't even exist just 250 years ago.
When the founders gathered to sign the Declaration of Independence, glaciers reached all the way into Icy Strait. Glacier Bay had not yet been born. By 1800, the bay was 5 miles deep. When John Muir visited in 1879, the bay had grown by another 40 miles. Since then, it has expanded another 20 miles, as the glaciers continue to retreat.
For travelers, that means that getting to the glaciers takes time. But there is plenty to see along the way. South Marble Island, for example, provides a safe place to breed for Black-legged Kittiwakes, Tufted Puffins, Horned Puffins (much rarer in these parts), Pigeon Guillemots, Common Murres, and other feathered critters.
It's also a spot where adolescent sea lions play king of the mountain.