Section 25. The entrance or discharge into the coastal waters, or the tributaries of such waters, of sewage or any other substance which might be injurious to the public health or might tend to contaminate any shellfish areas or shellfish therein which may be determined by the director to be of commercial value, or injuriously affect the fisheries therein, is hereby prohibited; provided, that this section shall not be deemed to interfere with the exercise of any right of drainage which had been approved by the department of public health prior to January first, nineteen hundred and forty-two, or in any drainage thereafter approved by said department or the department of environmental protection; provided further, that before granting such new approval the commissioner of environmental protection shall have consulted with the director as to the value of the marine fisheries involved. The provisions of this section shall not apply to any such entrance or discharge of heated effluent authorized under the terms of a permit for such entrance or discharge issued pursuant to state or federal water pollution control laws.