You get used to where you live and know how to cope with its problems. You become "street wise". When you move to another environment, you meet different hazards. It's best not to learn by experience. I'll confine my remarks to hazards that are peculiar to Australia and similar countries.
Heat Exhaustion: The technical term is hyperthermia, which is often confused with hypothermia. The first refers to the body having too much heat. The other is the exact opposite. Here, I'm talking about too much heat. The problem comes on quickly and can have serious consequences. The symptoms are extreme weakness and lack of coordination. Avoid hyperthermia by drinking plenty of water and staying cool. Treat it by cooling the patient and giving drinks. Recovery is usually rapid. If it is not, seek medical advice. Children have died of hyperthermia when left in cars. It is a serious offence in Australia to leave a small child in a parked car.
Land animals (big): Local authorities don't put up warning signs for fun. Signs cost money and are there for a purpose. I had a guest who thought a sign showing a swimmer being chased by a crocodile was a tourism gimmick. It wasn't. A few weeks earlier a family lost their dog to a croc while picnicking at that very spot.
Land animals (medium): Australia is home to some of the world's most venomous snakes yet most Australians rarely encounter one. I've never seen a snake in my garden. I see them occasionally when bushwalking and I see a lot when I go trout fishing. The Australian bush is full of snakes. Trout fishermen see them because they creep around and don't make their presence felt. I thump around when I go bushwalking. That way snakes are likely to hear me and get out of my way. The danger times are when the snakes are inactive. That happens in early spring when they are coming out of hibernation, in the cool of the day and when they are casting off a skin. I take a snakebite kit with me when I go walking. For more: http://www.healthdirect.gov.au/snake-bites
Land animals (small): Our scorpions have a nasty sting and some of our spiders are deadly. When camping, I'm careful to shake out my shoes before putting them on and I wear gloves when gardening.
Sea animals: Australian beaches harbour more perils than those in the colder parts of the world. Added to the danger of drowning we have a variety of marine animals that can cause injury and death. These include sharks, jellyfish, stonefish and the blue ringed octopus. The latter is small, pretty and deadly. Warn children not to touch them’
Despite the hazards, you can swim in safety. Our main beaches are protected by shark nets and patrolled by lifeguards. I recommend that you do not swim elsewhere without expert local advice. I've had some close encounters with sharks (of the white pointer variety) and have a lot of respect for them.
Remember that the box jellyfish (pictured above) is common on tropical beaches during the summer months. It causes death within minutes and claims victims most years. The treatment in CPR followed my medical evacuation. Of all the risks, it is potentially the most serious. Don't swim in tropical coastal waters in the summer without full-body protection.
Wild fires: Australia is a land or extremes. Flood is followed by drought. Vegetation grows abundantly and dries out. Native trees are packed with combustible oils. Fire danger goes through the roof periodically. Fire bombs are created in the mist of oils that collects above trees, particularly gum trees. Fires can flash across immense distances at unbelievable speeds. National Parks authorities shut parks when the danger of fire is high. They are not there to warn you in other areas and you must exercise your own discretion on bush walks and picnics.