Section 41. If such vessel or other obstruction is not removed within the time specified in such notice, and in a manner and to a place satisfactory to the department, or if no such owner or other person upon whom notice can be served is known to the department, it may remove such vessel or other obstruction, or complete the removal thereof, or cause the removal to be made in such manner and to such place as it deems best; and the necessary cost and expenses of such removal, if not paid by some owner or other person liable therefor, shall, when certified by the department and approved by the governor and council, be paid by the commonwealth.