Swan River

The River
The Swan River is the main waterway in Perth Western Australia. Sixty seven kilometres inland from the river mouth the Swan changes name to the Avon River. The Swan and Avon combined are over 280kms long before emptying into the Indian Ocean.
History
The Whadjuk Noongar people have inhabited the region surrounding the Swan River for over 40,000 years. They believe the river was created by a 'snake like' being called Waugal.
In 1697 VOC Dutch explorer Willem de Vlamingh named the river after the black swan, Cygnus atratus. The first European to sail up the river was the French explorer Nicholas Baudin in 1801. The Swan River Colony, now Perth, was established in 1829.
One of several significant events that have changed the river since the arrival of Europeans, was the widening of the river mouth in 1895. This has led to far greater levels of salt water entering the river.
Future
Check the Swan River Trust Healthy River Program.
Environment & Pollution
Algal blooms are a natural event resulting from high nutrient levels in the river. Nutrients usually enter the river from rural and urban run-off during rainfall. At times the nutrient levels in the river build up and are not 'flushed' as per normal. Blooms are basically high levels of algal growth. Some algae are harmless and some species are toxic. At any time of year the river can have a 'slight' to 'high' green tinge. As algal levels are normally higher after rain, it is recommended you don't swim in the river for 3 days. You can check algal levels here: Swan River Trust Algal Activity Report, and WA Health Department Healthy Swimming.
The Swan, passing through the most populated area in WA, is sometimes affected by toxic spills. You can check warnings and alerts here: Swan River Trust Current Alerts.
Occasionally as you descend, usually during winter, you may notice an 'oily' layer in the water, with almost zero visibility. This is not a bloom or the result of pollution, rather, it is the zone where the cold fresh river water mixes with the warmer salt sea water below.
River Hazards
Algal Blooms have been discussed earlier in this post. As have toxic spills.
The river is a busy place, as you expect in the middle of city with a population of 1.5million. Ferries, motor boats, yachts and kayaks, all moving about day and night. You should always use a dive flag, particularly at night with a strobe attached.
A number of marine species in the river have venomous defence systems, including cobbler, western rock cod and others. Best advice is to always keep you hands to yourself.
Wrecks can be dangerous places. Be careful of sharp rusting edges and broken glass buried in the silt around wrecks.
Always be aware of currents and tides. Some sites can have quite strong currents, particularly Jerrat Drive and Blackwall Reach.
The river can test your navigation skills. Apart from currents, reduced visibility from silting up can find you passing your wreck. Make sure you don't wonder into the main channel.
Swan River Dive Sites
Bicton Baths
Blackwall Reach
The Coombe
Glyde Street
Jerrat Drive
Swan Links
Swan River Marine Life
Swan River Trust
Swan River Trust Algal Activity Report
Swan River Trust Current Alerts
WA Health Department Healthy Swimming
Marine Life Links
Sea Slug Forum
Australian Museum Online site with information on nudibranchs, bubble-shells, sea hares and other sea slugs.