Whats all this about classes?

5.1 (1) Despite section 5, a work may be built or placed in, on, over, under, through or across any navigable water without meeting the requirements of that section if the work falls within a class of works, or the navigable water falls within a class of navigable waters, established by regulation or under section 13.

so what is section 13?

328. Section 13 of the Act is replaced by the following:
MINISTERIAL ORDERS
13. (1) For the purposes of section 5.1, the Minister may, by order,
(a) establish classes of works or navigable waters; and
(b) impose any terms and conditions with respect to the placement, construction, maintenance, operation, safety, use and removal of those classes of works or works that are built or placed in, on, over, under, through or across those classes of navigable waters.
(2) An order under subsection (1) (a) is not a statutory instrument within the
meaning of the Statutory Instruments Act; and
(b) shall be published in the Canada Gazette within 23 days after the day on which it is made.
(3) An order may incorporate any material by reference, regardless of its source, either as it exists on a particular date or as amended from time to time.