Do's and don't
Andaman & Nicobar Islands have many sandy beaches and coral reefs.  But only some of these beaches are supervised for safe swimming, snorkeling and diving.  Though Andaman water is generally safe for swimming and looks inviting, it also has some potentially dangerous marine animals, which may come in conflict due to mistaken identity such as prey or to defend their territory.  Though such incidents are extremely rare, visitors are advised to observe the following precautions for a safe and enriching swimming experience.
Do's
Find out about safe swimming or diving area from the Tourist Information Center, Local Tour Operators and Forest Department Staff.
Do not swim in Protected Areas to avoid dangerous animals.
Look for the safety sign boards. They help you to identify potential dangers.

Ask a lifeguard on duty for some advice on swimming conditions like local currents, tides, visibility, and the presence of dangerous marine creatures etc.
Swimming conditions can change quickly, so seek prior advice from a lifeguard before entering in water in an unpatrolled area.

Get a friend to swim with you so that you can look out for each other's safety and get help, if needed. 
Children should always be supervised by an adult.

Avoid swimming in the dark.
Raise your hand up for help if you get into trouble in the water.
Stay calm and wave your arm for help.

Carry minimum baggage for a comfortable tour.There are no porters in Havelock and Neil.  You can drop the extra baggages in your Port Blair hotel.

Be on time. The ferry, Cruise, island boats, Baratang convoy, Light & sound show etc have fixed timings.

If you are late you miss the tour and there are no refunds for no show or last moment cancellations.

Wear life jacket. Always wear the life jacket for your safety. Remember your life is precious than your selfie or comfort. Remember you are being watched by the Tourist Safety Enforcement Team (TSET) and can be fined or denied to board the boats without life jackets.

Follow the safety Instructions. While in sea observe the safety signs and adhere to the instructions of the life guards. Take special care of your children and elders. Do not venture into no swimming zones and do not disturb the marine eco system.

Don't
Do not dangle your arms or legs in the water during boat rides.

Do not swim under the influence of drugs or alcohol.

Shiny jewellery or bright colored clothes resembles fins of small fishes and may attract predatory fishes. Avoid such accessory or clothing while swimming.

If you have an open wound, please avoid swimming. Many predatory fish are attracted to blood odour.

Avoid diving or swimming amongst school of fish. This may attract predatory fishes such as sharks.

Avoid night swimming or diving.
Jelly Fishes   :   Their sting may cause pain and giddiness.  Don’t touch or play with them.  Get ashore if you see a large school of Jelly Fish.  In case of a sting, apply vinegar or an ice pack. Do not rub.

Sharks   :      Normally present in open sea and some parts of coral reef areas.  Avoid swimming or diving alone and don’t enter the water with open wounds.

Sea Snakes   :   Some sea snakes are poisonous and are usually recognized by their paddle-like tail.  They can be aggressive if handled or stepped on.  Stay well away from them.

Stone Fish   :   Present in shallow coral and rocks or camouflaged in mud and sand.  It has venomous dorsal spines and its sting could be lethal.  To avoid sting never walk on coral reef area.  Never lift rocks or corals.  Wear sturdy sandals while walking in shallow coastal waters.

Salt water crocodiles: Noticed in creeks, mangrove areas, sheltered waters and mouths of creeks.  Please avoid swimming or diving in these areas.  If you spot a crocodile, get ashore and alert the authorities. Crocodiles also move large distances in the open sea and can be found in coral reefs as well.
Look out for harmful marine animals