Answer
Some hotels feature indoor or covered pool amenities; dedicated indoor waterpark options are more limited than in some other resort regions. Call your property about pool status during storms. Never swim outdoors in lightning.
Sources: Visit Ocean City · NWS Wakefield / NOAA
Editorial visitor guidance for Ocean City, Maryland. Confirm current Town of Ocean City, Maryland DNR, NPS Assateague, and NWS rules when regulations or safety apply.
