The channel is navigable by large ships, only from the southeast, as far as the Douglas Bridge, approximately 9.7 miles (15.6 km). Between the bridge and Juneau International Airport, approximately 8.1 miles (13.0 km), it is navigable only by smaller craft and only at high tide.
The channel is becoming increasingly unnavigable due to shallow water depths. The two principal causes for this are:
If current trends continue, Gastineau Channel may eventually become dry or unnavigable or both.
During isostatic rebound, the Earth's lithosphere (crust) is slowly rising because of buoyant forces, following the removal of a large mass on the surface. This can be likened to an ice cube floating in a glass of water with a penny sitting on top. The weight of the penny makes the ice cube float lower, similar to the immense weight of a glacier on top of the lithosphere. When the penny (glacier) is removed, the ice cube (lithosphere) "rebounds" and floats slightly higher. In the geologic case, that scenario happens very slowly. Rates of isostatic rebound throughout SE Alaska vary from 0.1 to 1.5 inches/year depending on glacial history. The approximate rebound rate in the Juneau area is 0.25 to 0.5 inches/year.[4]
^Motyka, R.J. (May 2003). "Little Ice Age Subsidence and Post Little Ice Age uplift at Juneau, Alaska, Inferred From Dendrochronology and Geomorphology". Quaternary Research. 59 (3): 300–309. Bibcode:2003QuRes..59..300M. doi:10.1016/S0033-5894(03)00032-2.