That is a very fair question especially if you pull up a map and look at all the dams there are on the Columbia, Snake, etc., Eastern Washington/Western Idaho is littered with them. Here's a link to all the dams in the system; if you 'click' on the dam site it will give you data, including if it has a fish ladder(s).
http://www.nwcouncil.org/library/200...-1/default.htm
I would appear that the further upstream you get the less likely they built fish ladders.
fae