In St. Louis county the board of county commissioners may appropriate and expend from the general revenue fund, such amount, not to exceed $75,000 annually, as it shall determine for the following purposes:
(1) for the improvement of trails and portages on established canoe and boat routes dedicated to public use lying wholly or partially within the county;
(2) for the cleaning, deepening, widening and straightening of the bed of any river or creek to prevent flooding of lands; and
(3) to improve navigable lakes within the county and to mark by buoys and other means, reefs and shallow places in such lakes.
The powers enumerated in this section shall be exercised in accordance with the requirements, if any, of chapter 103G.