The Chicago Police Department routinely delays reporting police-involved shootings longer than it should, waiting about half an hour on average to tell the city’s Independent Police Review Authority about shootings by officers last year, according to a new report from the police watchdog agency.

Last year, the agency opened investigations of 24 shootings by officers — including a suicide the police didn’t notify IPRA about for more than six hours, the report says.

Taking that out of the equation, the average notification time was about 34 minutes for police-involved shootings, according to IPRA, which investigates shootings by Chicago cops and allegations of police misconduct and conducts probes.

In at least three of the police-involved shootings, the department notified IPRA that shots were fired at an officer but failed to say that an officer had fired a gun, too. The police are supposed to alert the agency as soon as it’s clear that an officer fired a weapon, according to the watchdog agency.

“More troubling is the fact that IPRA did not receive notifications of two of these incidents,” the IPRA report says.

Though it was posted on Jan. 13, the IPRA report was buried amidst bigger news involving the police. That was the same day the Justice Department, as expected, released a harsh assessment of the police department, finding that officers have engaged in a pattern of excessive force and calling for reforms of practices covering everything from training to supervision.

IPRA said officials in the police department and the city’s 911 emergency communications center have agreed to streamline the process for reporting police-involved shootings, aiming to reduce the average notification time on such shootings this year to 10 minutes.

IPRA said in a written statement Friday that it’s important to “be notified as soon as possible so that critical preliminary investigative steps, including identifying potential witnesses, preliminary canvassing or overseeing evidence collection, are not compromised.

“In essence, the sooner IPRA is notified, the sooner investigators will get to the scene to ensure that all necessary investigative activities are conducted promptly and independently.”

The Department of Justice’s report also was critical of IPRA, which Mayor Rahm Emanuel previously had announced will be replaced later this year by a new agency, to be called the Civilian Office of Police Accountability. The Justice Department report said IPRA is woefully understaffed and that its investigators are under-trained.

IPRA’s budget provided for 59 investigators and 11 supervising investigators in 2016. But at year’s end, only 45 investigators and four supervising investigators remained on the agency’s staff.

Once the mayor announced last summer that he was going to close IPRA and replace it, employees started jumping ship.

Meanwhile, more than 1,500 people have applied to work for COPA, which will have a budget for 141 full-time employees — compared with 97 full-time employees at its predecessor.

IPRA’s annual report also noted that complaints against officers fell in 2016, following four years of decreases. But there also was a similar drop in arrests over the same period, which could suggest that complaints fell because citizens were having fewer interactions with cops.

Another issue involving the relationship between the Chicago Police Department and IPRA is “who controls the scene” of shootings by officers, according to a knowledgeable source who spoke only on the condition of not being named.

“I think there needs to be something established about who has the lead,” the source said. “It’s a real issue.”

Other agencies also have seen delays in being notified by the Chicago Police Department about police-involved shootings:

• The Cook County medical examiner’s office has said the police waited more than three hours before telling the agency that an officer fired the shots that killed Quintonio LeGrier and Bettie Jones on the West Side the day after Christmas 2015. By then, too much time had elapsed for a medical examiner’s investigator to be able to gather useful information from the scene.

• Firefighters and paramedics also weren’t told LeGrier, 19, and Jones, 55, had been shot by an officer, authorities said. A lawyer for LeGrier’s father, who is suing the city, has said that suggests something wasn’t “on the up and up from the beginning.”

The LeGrier and Jones shootings remain under investigation by IPRA.