Don't buy more than you need. Reseal and keep for future use. Tide grids should not be used for sanding, scraping or painting. If other options are not available, use a groundsheet to collect spills as well as residue from sanding or scraping, then dispose of this properly. Have your boat hauled out annually and plan to do any substantial work on dry land, where you can contain waste products and keep them out of the marine environment.
Any foreign substance entering the water can hurt marine life.
To minimize the risk, you should do most of your work on land. Follow these steps when minor dockside work can't be avoided- check with your marina for its policy on this. Choose water-soluble solvents. Ensure that sanders, grinders and other tools have dust collection fittings in place. Always have absorbent pads or rags on hand to contain spills.