The report says scientists don't know enough about the effects on wildlife.
Activists are pushing to bring their quest to limit oil and gas development to the voters.
The Colorado Oil and Gas Conservation Commission announced Thursday that the well east of Greeley has been determined to be "potentially related" to two small earthquakes in May and June.
The governor spoke out a day after he abandoned the effort to find a legislative compromise to keep the measures off the November ballot.
Gov. John Hickenlooper had worked with a team of "willing partners" on legislation that would have granted more control to local municipalities.
The governor is trying to broker a deal to avoid ballot measures restricting drilling. A key interest group signed on amid controversy, but some legislators are unsupportive.
A new study links the spike in earthquakes in central Oklahoma to huge amounts of wastewater pumped underground by oil and gas operators.
Supporters of ballot measures to give more control to local governments over drilling will be able to gather signatures for all six of their proposed measures.