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DENVER — Voters have narrowly passed a ballot measure making Colorado the 19th state to legalize sports gambling, with the new tax revenue slated for water conservation projects.

The measure allows the parent companies of Colorado’s 33 casinos in Black Hawk, Central City and Cripple Creek to offer onsite and online betting on professional, collegiate, motor and Olympic sports starting in May.

The ballot question had little opposition, but the election results were so close that the outcome could only be determined Wednesday as the final votes were tallied.

With nearly 90% of the vote in, the yes vote was leading by more than 23,000 votes, 50.8% to 49.2%.

Legal sports betting has grown since New Jersey won a U.S. Supreme Court case in 2018 allowing all 50 states to offer it.

Colorado joins five other states that passed legal wagering this year: Illinois, Montana, New Hampshire, North Carolina and Tennessee.

Sports gambling is also set to become legal in Maine next year, and it’s allowed in the District of Columbia and Puerto Rico.

The Colorado proposal calls for a 10% flat tax on net sports betting proceeds, which is estimated to total about $11 million in the next financial year that starts July 1.

State lawmakers passed a bill earlier this year allowing the Colorado Water Conservation Board to use that money to award grants to help meet the state’s water plan.

The plan, launched by former Gov. John Hickenlooper’s administration, sets long-term goals to meet the needs of a growing population, agriculture, outdoor recreation and obligations to Southwestern states that rely on the Colorado River.

Channeling the sports betting tax revenue to the water plan won the support of environmentalists and farming groups, but the money generated is expected to fall well short of the water plan’s estimated price tag of $100 million a year.

That’s in line with the limited revenue seen by most other states that have already legalized sports wagering.

An Associated Press analysis shows that seven states that reported on sports betting revenue for the fiscal year that ended in June generated a total $74 million in state taxes — a drop in the bucket for state budgets.

Reasons varied, from slow rollouts to the unavailability in some places of mobile betting.