A senior police officer, investigating the case said that the Chief inspector of boats, M Mathew, was arrested
M Mathews was held on the directions of crime branch IG Sreelekha. The police also arrested the temporary watcher Prakash for allowing the boat to be overloaded.
Earlier, police had arrested the steerman and a subcrew in connection with the mishap.
45 persons, mostly tourists from outside the state, had drowned after the ill-fated boat 'Jalakanyaka' overturned in the lake near the Periyar Wildlife Sanctuary in Idukki district.