WATERVILLE — The Colby and Bates College communities are mourning the loss of one of their own Friday.

Head Colby men’s lacrosse coach Jack Sandler, a 2002 Bates graduate and former assistant coach there, died suddenly Thursday. He was 35.

According to Colby College officials, Sandler was on a recruiting trip out of state. He reportedly collapsed while on a treadmill in a hotel.

“I have had the privilege of knowing Jack since I arrived on campus and have been so impressed with his warmth, vitality, deep integrity, and genuine concern for his students,” Colby President David A. Greene said in a news release. “It was clear he loved the game of lacrosse and coaching, but his real passion was teaching and helping students develop their full potential physically, intellectually, and personally.”

Sandler was in his third year as head coach of the men’s lacrosse program. Colby finished in last place in the New England Small College Athletic Conference and lost a good recruiting class in 2013. Sandler took over the program for the 2013-14 academic year and guided the Mules to two straight NESCAC playoff appearances.

Sandler was 15-15 overall at Colby and his program was extremely popular. He had more than 50 student-athletes try out for the team in 2015.

Colby players Derek Youngman, Tyler Will, and Austin Sayre earned United States Intercollegiate Lacrosse Association (USILA) Honorable Mention All-American honors after the 2015 season. Sayre also was the NESCAC Rookie of the Year in Sandler’s first season in 2014.

Sandler came to Colby after eight seasons as head coach at Skidmore College.

“Jack was a truly great, trusted friend. More like a son in many respects,” Bates head coach Peter Lasagna said in a release.

Lasagna coached Sandler and then hired him as an assistant coach.

“I am deeply saddened by the loss of this great young man and dear friend,” Lasagna said.

A Long Island native, Sandler was a four-year starter for the Bobcats and finished as the program’s second all-time leading scorer with 199 points. Sandler was the 1999 NESCAC Rookie of the Year and earned All-NESCAC honors during his career.

Sandler spent two seasons as an assistant coach for Lasagna. He also spent one year as an assistant coach at Dickinson College.

Sandler was the Liberty League Coach of the Year in 2007 and 2011 in his career at Skidmore. He led the Thoroughbreds to a regular season title in 2011 and appearances in the conference title game in 2007 and 2010.

Sandler also was highly involved with lacrosse on the national level. He sat on the USILA Executive Board as an NCAA Division III representative. Sandler was elected to the post. He also was part of the USILA All-America Selection Committee from 2011 to 2013 and has served on the NCAA Regional Advisory Committee from 2007 to 2010.

“We have been incredibly fortunate that Jack has been such an integral part of our community,” Greene said. “I join others who will miss him greatly, and our thoughts are with his players, colleagues, and family.”