Any persons, firms, and corporations engaged in the transportation of freight, passengers, or express, by water, wholly within this state, shall, within 30 days after this act takes effect, make and file, in the form prescribed, its schedule of rates, fares, and charges for the carrying of freight, passengers, and express. The filed rates, fares, and charges continue in force until superseded by other schedules filed with the department of state police as provided in this section. The department of state police shall make a decision on all filed rates, fares, and charges within 30 days after the rates, fares, and charges are filed. The department of state police may, either upon request or upon its own motion, suspend the operation of any filed rate, fare, charge, or tariff for a period not exceeding 30 days. If a filed rate, fare, charge, or tariff is suspended by the department of state police, the department shall give the interested carrier immediate notice of the suspension and shall, within 10 days from the date of the suspension, set a hearing date not more than 20 days from the date of the suspension. The department of state police shall give notice of the hearing date to the carrier and to other interested persons. After the hearing, the department of state police shall set the rate, fare, charge, or tariff in the matter complained of, and that rate, fare, charge, or tariff continues to be the legal rate, fare, charge, or tariff in force until superseded as provided by law. Any ferry company operating within any municipality under an agreement with that municipality is not affected either as to fares or as to operation by this act.