A Chicago Park District worker resigned this week after officials said he was accused of having “an inappropriate relationship with an underage former seasonal employee,” a parks spokeswoman said Wednesday.

The park district declined to name the employee but said he quit Monday. This is the fourth park district worker known to have resigned after being accused of serious sexual misconduct, according to parks officials.

The man who quit was a 31-year-old supervisor at Humboldt Park at the time of the alleged misconduct and the girl involved was a 16-year-old lifeguard, according to a source familiar with the case who was not authorized to speak publicly.

Earlier this year, the inspector general’s office corroborated accusations against three senior lifeguards, according to documents obtained by WBEZ.

The resignation came as law enforcement authorities became increasingly focused on sexual misconduct targeting lifeguards at Chicago’s beaches and pools – some of whom are as young as 15 when they start working during the summers for the park district.

WBEZ first reported in April that the park district’s inspector general was investigating complaints against dozens of employees accused of engaging in sexual harassment, abuse and assault against co-workers in the agency’s Aquatics Department. An investigation by the station has revealed more allegations of endemic sexual violence against young female lifeguards going back decades.

But last month, Park District Inspector General Elaine Little resigned after WBEZ revealed that she was herself the subject of an investigation at the time she left her previous job at the Cook County juvenile jail. The park district hired an outside law firm to continue investigating lifeguard abuse – and to review officials’ own handling of the sensitive issue.

Cook County State’s Attorney Kim Foxx also has opened an investigation, urging survivors of sexual abuse at the park district to call a hotline number set up at her office this week, at 312-603-1944.

Chicago Police said Wednesday no arrest has been made in connection with the alleged incident involving the parks employee who resigned this week.

Parks officials say they were “made aware” of the alleged relationship with an underage former seasonal worker on Aug. 26, with the details provided by a “third party complainant.”

At first, officials say, the complainant “could not be reached and the alleged victim … refuted being subjected to any misconduct.”

But on Sept. 10, the complainant provided the park district with a statement backing up the allegations. According to park district officials, that statement contained “screenshots of text messages which include reports of inappropriate communications and choking done in a sexual manner.”

Three days later, officials say they suspended the accused employee and took steps to fire him.

The situation increased pressure on the park district’s embattled CEO, Michael Kelly, and the parks board’s politically connected president, Avis LaVelle.

Influential 32nd Ward Ald. Scott Waguespack – who has called for the removal of Kelly and LaVelle over their handling of the lifeguard abuse scandal – on Wednesday issued a statement blasting the park district for its description of the alleged relationship between the employee who resigned and the underage lifeguard.

“I reiterate my call for Mike Kelly’s resignation and that of all Park Officials who have failed these victims,” Waguespack said. “To be clear, we are not talking about ‘relationships,’ we are talking about rape and sexual abuse. We are talking about a culture where grooming and other predatory behaviors are swept under the rug.”

Ald. Michele Smith, 43rd Ward, also called on Kelly to resign Wednesday. She became the third member of the City Council to take that position, following Waguespack and Ald. Rossana Rodriguez-Sanchez, 33rd Ward.

Dan Mihalopoulos is an investigative reporter for WBEZ’s Government & Politics Team. Follow him on Twitter @dmihalopoulos.