“But officials say that putting the fence right up against the river could interfere with its flow during a flood and change its course, illegally altering the border”
Looks like environmentalists at work to me, getting a two-fer here by destroying public property and discrediting border control efforts.
Maybe, but I don't see how a fence right along a river bank would work from purely engineering perspective. You need to be able to access it easily for repairs, maintenance, etc, and that requires access roads on both sides of the fence.