Whether or not the fence is legal requires more clarification of the CRS. Although the fence seems to fit the definition of criminal obstruction, such terms as "waterway" and "substantial group of the public" may require further definition. That could come by one of two means:
1) Legislation to clarify CRS § 18-9-107
2) Legal proceedings brought by either the landowner or recreational boaters.
Note that this is the same section of river that was involved in a legal dispute several years ago which was settled out of court- I do not know what the terms of that settlement were.
Also note that any party who touches the fence could be found guilty of criminal trespass, regardless of weather or not the fence is an obstruction.
Several years ago, the CWWA and AW reached a settlement with landowners on the Deckers section of the South Platte in which the landowner removed an obstruction with the stipulation that boaters on that section of the river not touch the banks or stream beds, which is defined as criminal trespass in CRS § 18-4-504.5
To find out more about Deckers go to:
and click on "River Access" on the left.