Answer
Chiang Mai is an inland northern Thailand destination, so it does not have local beaches or offshore islands. For a water-focused day around Chiang Mai, compare waterfalls, hot springs, riverside areas, hotel pools and lakes; for a genuine beach trip, plan separate travel to southern or eastern Thailand.
Practical Chiang Mai planning note: Look at the qualifications, safeguarding, facilities, language support and suitability for your own health or family needs. A pleasant online description is not a substitute for checking the current programme and speaking directly with the provider. Confirm that any named venue still operates and check its present opening days, booking method and location directly. Chiang Mai is inland; beach and island experiences require travel to another region, while local water-based alternatives include rivers, lakes, waterfalls, pools and hot springs.