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. 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.