I believe it is technically illegal:
C.R.S. 18-9-107. Obstructing highway or other passageway.
(1) An individual or corporation commits an offense if without legal privilege such individual or corporation intentionally, knowingly, or recklessly:
(a) Obstructs a highway, street, sidewalk, railway, waterway, building entrance, elevator, aisle, stairway, or hallway to which the public or a substantial group of the public has access or any other place used for the passage of persons, vehicles, or conveyances, whether the obstruction arises from his acts alone or from his acts and the acts of others; or
(b) Disobeys a reasonable request or order to move issued by a person the individual or corporation knows to be a peace officer, a firefighter, or a person with authority to control the use of the premises, to prevent obstruction of a highway or passageway or to maintain public safety by dispersing those gathered in dangerous proximity to a fire, riot, or other hazard.
(2) For purposes of this section, "obstruct" means to render impassable or to render passage unreasonably inconvenient or hazardous.
(3) An offense under this section is a class 3 misdemeanor.
Good luck ever getting this enforced. If it did get enforced, the ranching lobby would quickly get an exception passed in the state legislature, I'm sure. Just a fact of life for the western boater.
Join up, suckas.
"People demand freedom of speech to make up for the freedom of thought which they avoid."
- Soren Kierkegaard