Western Australia is the largest State in Australia and comprises about 40 per cent of the continental coastline of Australia. It spans many climatic zones from the humid tropics north of North West Cape to the cool and arid South Coast in the Great Australian Bight. The temperate and tropical waters overlap in the middle between Cape Leeuwin and NW Cape. Big westerly swells means that the coastline is often blasted with high wave energy.
Inshore areas are usually free of currents with only offshore areas are susceptible to moderate wind generated currents of usually less than one knot. Inshore areas with restricted water passages, such as between reefs and islands can experience localised currents, some dangerous. Usually swimming conditions are safe on a calm day with low swells.
The summer is popular for water activities and underwater visibility is good rather than at its best. The Autumn creates the most stable and moderate conditions and is the best dive for on water activities. Swells tend to be more moderate and the visibility underwater improves. In Winter the winds are unpredictable and swing around as cold fronts pass over. The seas rise and swells are often dangerous for water activity. An occasional slow moving high can bring brief patches of exceptional weather although the swells can still be uncomfortable. With the onset of Spring algal blooms can cause cloudy waters as the days become long and sunny and the waters warm. The swells tend to persist with diminished strength until Novembers
The temperate and sub-tropical waters of Australia enjoy high levels of species endemism (uniqueness) and WA is no exception. In addition to wholly new species like western king wrasse and western rock lobsters, even the species that are common across Australia are often isolated populations or slightly different sub-species from their eastern counterparts. Tropical species further north tend to be more widespread throughout the Indo-Pacific region. What they lose in diversity they make up for in size, numbers and colour.