I wouldn't wear contacts while snorkeling.
Remember that water has a natural magnifying effect, and that should help.

If you really want to do it right, you can go to a local dive shop and get a snorkel mask that is quasi prescription. A good shop can take your glasses, read them on a machine, and from there, determine what magnification of snorkel lens is best for you.

You can also get actual prescription ground lenses, but those are considerably more.

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