In Re the Application for Water Rights of Lazy D Grazing Association in Weld County. Opposers-Appellants v. Lazy D Grazing Association, Applicant-Appellee City of Sterling and City of Fort Collins, and Basin Lands, LLC; Bijou Irrigation Company; Bijou Irrigation District; Cache La Poudre Water Users Association; City of Boulder; City of Englewood; City of Greeley, acting by and through its Water and Sewer Board; City of Thornton; L.G. Everist, Inc.; Northern Colorado Water Conservancy District; Mary Estabrook; State Engineer and Division Engineer for Water Division No. 1; and United Water and Sanitation District. Opposers-Appellees, 2024 CO 63

Lazy D Grazing Association manages a large ranch (about 25,000 acres) on the Colorado-Wyoming border with little access to surface water, limited to seasonal streams.
In 2020, Lazy D applied for a court determination that groundwater beneath its ranch (in the Upper Laramie Aquifer) is "nontributary", meaning its use would not affect natural stream flows within 100 years above a defined threshold.
Nontributary groundwater in Colorado is not subject to the prior appropriation doctrine and can be used by the landowner without impacting other water rights.
The application drew opposition from various municipalities and organizations, but only the Cities of Sterling and Fort Collins ("the Cities") remained as opposers at trial.
The State Engineer issued a factual determination supporting Lazy D's claim. At trial, both sides presented expert testimony on whether the aquifer was hydraulically connected to streams.
The Water Court ruled for Lazy D, finding the groundwater nontributary by clear and convincing evidence. The Cities appealed to the Colorado Supreme Court.

Issue	Plaintiff's Argument	Defendant's Argument	Held
1. Scope of State Engineer's Authority	State Engineer can't conclusively determine nontributary status and court shouldn't give such findings special weight	State Engineer’s findings on facts get a rebuttable presumption, but not legal conclusions	State Engineer can make factual findings but not legal conclusions; trial court's harmless error to presume otherwise
2. Burden of Proof	Court wrongly shifted burden to Cities to prove groundwater is tributary	Lazy D, as applicant, bore the burden throughout to prove nontributary by clear and convincing evidence	Court did not shift burden and correctly found Lazy D met its burden; any wording error was harmless
3. Use of Evidence Outside the Record	Court improperly relied on scientific materials not in evidence or personal knowledge	Court properly used secondary sources only for background or to assess expert authority, not as evidence	Court’s references were permissible for context/explanation, not error
4. Expert Witness Weight	Court failed to explain why Lazy D’s expert was more credible than Cities’ expert	Court provided sufficient reason for assigning more weight to Lazy D’s expert	Court sufficiently explained its weighing of experts; admissibility and credibility were properly handled

City & Cnty. of Denver ex rel. Bd. of Water Comm'rs v. Middle Park Water Conservancy Dist., 925 P.2d 283 (Colo. 1996) (factual findings by water court upheld unless evidence is wholly insufficient)
Wolfe v. Jim Hutton Educ. Found., 344 P.3d 855 (Colo. 2015) (questions of water law/statutory interpretation reviewed de novo)
Colo. Ground Water Comm’n v. N. Kiowa-Bijou Groundwater Mgmt. Dist., 77 P.3d 62 (Colo. 2003) (all groundwater presumed tributary absent clear and convincing evidence to contrary)