I'm probably mistaken, but I thought the rules stated that you had to continue the river after the spring goes down? Placing a river tile field to field against a previously placed river tile would not be extending the river...
On a completely separate note, does anyone else feel that it's silly that the River II rules say the fork has to be the first tile after the initial spring?
Agreed. This has always felt disappointing.
I think the reason for the fork is that it gives players different options for their tile placements. This was always a weakness of River 1 (imho) so the fork was introduced to fix this with River 2. But the effect is lost if the fork comes out late, so it makes sense to me that it should always be the first tile out after the spring.