At the posted coordinates, you need to launch a boat. Then, head on over to stage 2, where you will find a white water gauge. The water gauge is at the water level on the main bridge support. You can not do this from street level, you have to get on the river! This gauge is actually two signs, everything you need for this multi is on the top of the two signs.
To solve the final coordinates, assume: N45 14.ABC W093 31.XYZ
ABC = Take the top-right-most number on the top sign (nearest the top right bolt), remove the decimal point (e.g. 100.00 would become 10000), and subtract 269.
XYZ = Take the middle three numbers of the phone # (e.g. (...) ###-....) on the bottom of the top sign and add 196.
Please note - this cache is in a potentially dangerous location and seeking it is done at your own risk! I strongly recommend against doing this in the winter, as ice on rivers is always unpredictable. Legal entry points (PWAs) are provided, other entry points may be considered trespassing on private property. The terrain rating reflects the need to travel a significant distance on water.
You can validate your puzzle solution with certitude.