A helicopter flies Tuesday above the Sebasticook River in Clinton as part of the search for a missing 36-year-old man. After days of searching and no sign of Justin Howard, authorities on Friday decided to end the search. Rich Abrahamson/Morning Sentinel file

CLINTON — A search that concluded Friday for a man seen entering the Sebasticook River earlier this week was a challenge for divers who had to contend with frigid water temperatures, rapids and lack of a boat launch near where the man disappeared, according to a lead diver for the Maine Warden Service.

Authorities decided to end the search after days of looking for 36-year-old Justin Howard, who witnesses said was seen Monday running into the water near Pleasant Street in Clinton. About 18 divers with the warden service and other agencies were joined by a helicopter, airplane and dogs in the effort to find Howard.

Clinton police Chief Stanley “Rusty” Bell said the decision was made to end the search because there has been no sign of Howard after days of looking.

Bell said earlier that investigators had a preliminary understanding of what prompted Howard to enter the water and that Bell would provide that information this week. But he said Friday that more interviews with witnesses need to be done before such information is released. Howard is from the Waterville/Winslow area and was in Clinton visiting friends, Bell previously said.

Cpl. Tony Gray, who leads the warden service’s dive team, said divers at the scene had to contend with high water and fast currents. Although the conditions are common for this time of year, they can present dangerous situations for divers.

There are unique challenges to any search, Gray said, and in this case a leading problem was that the nearest boat launch was about four and a half miles downstream and there were sections of river with rapids. Boats were needed that could navigate past the whitewater.

The type and number of boats available to divers then affects the search because it determines how many people can be out at a time and how often boats have to bring out new divers. The divers in Clinton were able to use one jetboat and four airboats to get past the rapids.

“This particular search, the biggest challenge was getting the equipment and platforms that we needed to search on the river,” Gray said.

The water temperature this week was around 35 degrees Fahrenheit and that dictated how long divers could be in the water and how many dives they could undertake in a day, Gray said.

The warden service’s dive team does around five trainings a year, each of which can last up to five days. Those trainings focus on preparing divers for any condition in any setting. A new diver to the team undergoes two years of training to be considered fully ready, Gray said.

With a river search, there are concerns about underwater debris and divers getting caught in a current and being pulled away from the search team. To combat that, divers will wear a harness and the team on the boat will hold a rope connected to them, which also helps track the search pattern of an area, Gray said.

When approaching a search like the one in Clinton, divers first identify what are called “holding water,” places where the river has turned or the current has slowed. That makes the area safer to dive, and it’s likely that anything being carried downstream would stop in that area.

For a number of reasons river searches tend to be more challenging than lake searches, he said.

“Rivers are always — no matter what time of year — are a more challenging search than lakes and ponds are, but in particular with the cold water and the high water, it really adds on to it,” Gray said.