It cannot be said with certainty that it is more dangerous to be in the water in the Australian summer months because this is when most attacks have been recorded. Fact is that more people enter the water in the summer time, when it is warm and there are holidays. It cannot definitely be proven either that the most dangerous waters are South Australian waters due to the largest amount of sharks and shark attacks. There is also no proof that one is safer in clear water than in murky waters. There is simply no pattern regarding attacks, especially with great whites.
Every attack is different.
People tend to feel safe when there are dolphins around. Dolphins are nice and playful and friendly, they chase sharks away. This is a misconception as well. Dolphins are prey for sharks, they have been found in stomachs of captured specimen. In certain instances it can be that a big pod of dolphin defends its young and chases any intruding sharks away, but I am sure that would not deter a hungry white.