Oil and gas spills across Colorado increased in 2017 after two years of decline, with companies reporting nearly a dozen mishaps per week — including numerous leaks along pipelines and at least six cases in which hydrocarbons flowed directly into waterways.

A review of the latest state data also shows 22 incidents under investigation in which gas apparently contaminated domestic water wells.

The industrial spills disclosed to the Colorado Oil and Gas Conservation Commission show continuing environmental harm as the total number of active wells statewide surpassed 55,000. Oil and gas companies in 2017 produced oil and gas worth about $10.6 billion.

Their operations are concentrated in Weld County, north of metro Denver, with more than 23,700 wells. Garfield County in western Colorado has more than 11,400 wells. Closer to Denver, companies have drilled about 400 wells in Boulder County and 989 in Adams County.

State lawmakers created the COGCC to regulate oil and gas development while protecting people and the environment. In 2017, COGCC enforcers imposed an all-time high $7,166,851 in penalties for violations of rules.

On Thursday, leaders of Conservation Colorado, one of the state’s largest environmental organizations, raised concerns that spills increasingly degrade Colorado’s land, air and water and urged lawmakers to do more to deal with worsening cumulative impacts.

Companies reported 619 spills in 2017, state data show. Altogether, companies spilled more than 93,000 gallons of oil into soil, groundwater and streams. They also spilled more than 506,000 gallons of “produced water,” waste from drilling and hydraulic fracturing that emerges from deep underground and contains chemicals.

That number of spills reflects a 17 percent increase above the 529 spills reported in 2016, state data show. Total annual spills remained lower than the 792 spills in 2014 and 624 in 2015.

“We have concerns about any oil/produced water spill, which is why we have a regulatory system set up to ensure such spills are reported, investigated and cleaned up,” Colorado Department of Natural Resources spokesman Todd Hartman said.

The volume of oil spilled each year has decreased compared with the volumes spilled between 2009 and 2013, Hartman said, adding that this happened “with thousands of additional active wells added since that time.”

In at least six cases in which oil and gas spills directly contaminated rivers and streams, COGCC regulators notified Colorado Department of Public Health and Environment water quality officials.

State investigations of the 22 household water wells that may have been contaminated with gas are continuing because COGCC rules require companies to take precautions (using steel casing held in place by cement), in drilling and later abandoning wells, to guard against contamination of fresh water.

Some of the wells were located in agricultural parts of Weld County, according to a report provided to the water quality officials.

So far, the investigations “tell us that well integrity issues do exist in certain cases and do cause thermogenic gas impacts to the aquifer,” Hartman said. “But with thousands of water wells sampled in the (Denver-Julesburg) Basin, we also know that the problem is not ubiquitous or systemic throughout the basin. These are unique circumstances that the agency takes very seriously and makes every effort to investigate and stop the source of gas and ensure that the impacted party has a reliable source of safe drinking water.”

The Colorado Oil and Gas Association industry trade group did not immediately respond to requests for comment.

Conservation Colorado officials said lawmakers must do more to deal with environmental harm.

“The oil and gas impacts in Colorado are only getting greater. And they are not going to go away soon. There are myriad impacts. Damage to our water. Oil and gas well fragmentation of habitat. Air pollution caused by the leaking methane. Not to mention public health and safety,” said the group’s deputy director, Jessica Goad.

“People don’t feel like there’s a venue where change can be made. We’ve seen the oil and gas commission struggling to determine how to fix the issues of oil and gas pipeline mapping and the leaking. And we have not made progress in the legislature. Dozens of bills have been killed in the state Senate over the last few years,” Goad said.

Conservation Colorado has 36,000 members. It is focused on legislation that would require bigger buffers between industrial facilities and schools. It is also seeking to increase local control over industrial operations inside cities and increase health and safety protection for residents.