Arriving for first visit to Belize and Ambergris Caye on Feb. 20. During our stay, there will be a number of cruise ships arriving in Belize for day visits.
Is it advisable to avoid taking tours or snorkeling trips when the cruise ships are in port?
Here is what's coming:
Feb. 22 -- Glory (2,974 passenger capacity.), Norwegian Spirit (2,018), Norwegian Star(2,348), Ryndam (1,260).
Feb. 23 -- Legend (2,124)
Source: http://cruiseportinsider.com/belizeschedule2012.html
Appreciate any advice you can share.

Unless you like crowds It is probably best to skip mainland trips or trips to the cayes outside Belize City on cruise ship days. Snorkelling around Ambergris Caye shouldn't be a problem.