Colo. Rev. Stat. § 37-87-125
Any person proposing to construct a reservoir for the purpose of storing water, other than a reservoir specified in section 37-87-105(1) or a livestock water tank as described in section 35-49-103, C.R.S., shall submit notice thereof to the state engineer prior to the beginning of any construction. Such notice shall include the location of such proposed reservoir with reference to section, township, and range and the dimensions of the reservoir, the dam, and the spillway. If any reservoir is constructed without the notice required by this section, the state engineer may prohibit the storage of water in such reservoir or direct the withdrawal of water from such reservoir. The provisions of this section shall not apply to structures listed in section 37-87-114.5.
C.R.S. § 37-87-125