The Kalgan River was named the "Riviere des Francais" by the French Scientific Expedition in 1803, captained by French explorer Nicolas Baudin, in the ship Géographe, which anchored in what is now known as Frenchmans Bay, and was subsequently known as the "French River" by early settlers. The explorer Alexander Collie recorded the river as "Kal-gan-up" in April 1831. The name Kalganup is believed to be the Noongar word for "place of many waters".Kalganup is also thought to mean "place of fishes" and there are still the remains of Aboriginal fish traps to prove the point. The traps, known as the Albany Fish Traps have been situated here for many years.
The fringing vegetation of the estuarine portion of the Kalgan River is dominated by the saltwater paperbark trees surrounded by dense stands of coastal saw sedge and shore rushes. The downstream freshwater parts of the river have a much greater variety of species, with a fringing forest that includes swamp paperbark, marri, jarrah, wattle and Western Australian peppermint trees. Further inland, species such as swamp yate, flooded gum and varieties of Banksia and Hakea are found. Parts of the riverbank that have been cleared support a variety of introduced weeds that are shallow rooted. In areas in which the native deep-rooted species have been lost, erosion of the river bank has become a problem. Many wild flowers can be found along the Luke Pen Walk, a trail that follows the river for the 9 km before it reaches Oyster Harbour. Some of the varieties include Hovea trisperma (common hovea), Hovea pungens (devil’s pins), Hovea elliptica (tree hovea), Adenanthos obovatus (basket flower), Lysinema ciliatum (curry flower), Leucopogeon pulchelus (beard heath), Banksia sessilis (parrot bush), Banksia squarrosa (pringle) and Acacia extensa (wiry wattle).
The estuarine end of the Kalgan River is home for many species including black bream with a few skippy, herring, mulloway and whiting. Smaller freshwater species that can be found in the Kalgan River include the western galaxias (Galaxias occidentalis), the common jollytail (Galaxias maculatus), the mud minnow (Galaxiella munda), Balston's pygmy perch (Nannatherina balston), Nightfish (Bostockia porosa) and the western pygmy perch (Edelia vittata). The river is home to a large population of birds. In the estuarine part of the river, species such as the Australian pelican, little black cormorant, pied cormorant, pied oystercatcher, black-winged stilt, common sandpiper, Australian white ibis, straw-necked ibis, yellow-billed spoonbill, Pacific gulland Caspian tern can often be seen. The freshwater parts of the river also support an enormous variety of birds including nankeen kestrel, Australian hobby, wedge-tailed eagle, short-billed black cockatoo, long-billed black cockatoo, galah, little corella, purple-crowned lorikeet, red-capped parrot, laughing kookaburra, willie wagtail, white-breasted robin, splendid fairywren, New Holland honeyeater, red wattlebird and red-eared firetail.Amphibious species that can be commonly be found in and around the river are frogs, such as the western banjo and moaning frogs. Reptiles frequently found in the area include tiger snakes and dugites.
The southern end of the Kalgan River has two bridges of note: The Upper Kalgan bridge and the Lower Kalgan Bridge. The Lower Kalgan Bridge was built from 1906 and opened in 1908. At 900 feet (274 m) in length, it was the longest of its kind over water in the State at the time. At this time, the bridge had a special navigation span, 40 feet (12 m) wide at the deepest part of the river. The original bridge remained in place until 1958, when it was replaced, but the navigation span trusses were removed for preservation and are now on display in the park at the western end of the bridge.
The Government Jetty was also built in 1906 so that timber and other construction materials could e delivered adjacent to the Lower King Bridge site. The jetty was also later used as a landing point for tourist vessels that traveled upriver from Albany. It is now in a state of disrepair.
The Kalgan River contains many small islands, particularly in the section below the Upper Kalgan bridge. The largest is Honeymoon Island (also called Elbow Island), which is slightly upstream of the Lower Kalgan bridge. This island has a small clearing and can be readily landed upon. A smaller island, Willie Island, is a little downstream of the Upper Kalgan bridge.
The Kalgan River is a place of great significance to the local Noongar people. A dreaming story tells us of a husband and his wife who lived in the Porongurup ranges. The husband beat his wife terribly but she escaped from him by stumbling through the thick bushland. As the wife ran through the bush, her digging stick trailed over the Earth and cut open the soil behind her forming the path of the Kalgan river.