Like everything else inside the Barrier except living, magical people, the river was there, but it was a slightly different river from the "real" one.

Signum is nearly thrown by the roll, but hangs on tightly and endeavors to stab Laevatein into the dragon's hide, both to attack it and get a better grip. It's either that, or be thrown, and Signum doesn't like her chances anywhere but where she is right now.