(3) It shall be the duty of [ F121 SEPA ] to keep any maps deposited with it under subsection (2) above available, at all reasonable times, for inspection by the public free of charge. (4) In this section --  " miles " means international nautical miles of 1,852 metres; " loch or pond " includes a reservoir of any description; " relevant loch or pond " means (subject to subsection (5) below) any loch or pond which (whether it is natural or artificial or above or below ground) discharges into a relevant river or watercourse or into another loch or pond which is itself a relevant loch or pond; " relevant river or watercourse " means any river or watercourse (including an underground river or watercourse and an artificial river or watercourse) which is neither a public sewer nor a sewer or drain which drains into a public sewer. (5) The Secretary of State may by order provide --  (a) that any area of the territorial sea adjacent to Scotland is to be treated as if it were an area of relevant territorial waters for the purposes of this Part; (b) that any loch or pond which does not discharge into a relevant river or watercourse or into a relevant loch or pond is to be treated for those purposes as a relevant loch or pond. (6) The power of the Secretary of State to make an order under subsection (5) above shall be exercisable by statutory instrument subject