It is a large river that is connected to the Hyrule Castle Moat, Squabble River, and Zora River ultimately feeding into Lake Hylia and Nabi Lake. Floret Sandbar is located at the fork in the river where part of the river flows in Lake Nabi while the other half continues onward to Lake Hylia. The Sadbar is home to the Hila Rao Shrine though is also home to Magda and her garden of flowers which surrounds the Shrine. Rafts appear in certain locations along the river which Link can use to use the river as an alternative way of travel. However a Korok Leaf is required to move the Raft though Link can let the river currents move the raft along using the Korok Leaf to make minor adjustments as the raft moves downriver. However Link must work harder to sail the Raft against the current. As with most waterways, sunken Treasure Chests can be found in certain places which Link can remove with the Magnesis Rune. For example, a chest containing a Royal Shield can be found in the water near the Raft docked northeast of the Boneyard Bridge. Further downriver under the water northwest of the Orsedd Bridge is a chest containing a Royal Claymore.
Given its connection to several rivers and waterways, Zora such as Mei and Prince Sidon apparently utilize Hylia River to travel to more quickly by swimming which is a far more efficient way for Zora to travel around Hyrule allowing them to reach areas near the river such as Lake Hylia and Wetland Stable respectively as well as using the river to travel to Zora River then back to Zora's Domain. However the river does have some dangers such as Water Octorocks.
Several Koroks can be found hidden in certain areas of the river. Both the Riverside Stable and Wetland Stables are located close to the river. Orsedd Bridge, Rebonae Bridge, Horwell Bridge, Owlan Bridge, Eagus Bridge, and Proxim Bridge all span the river at certain points.
Hylia River is home to all three types of bass Hyrule Bass, Staminoka Bass, and Hearty Bass. Armored Carp and Mighty Carp can be found in certain areas of the river as well. Water Octorocks are apparently the natural predators of fish living in the river as they occasionally drop local fish types when killed. Ducks can be found swimming in the water and can be hunted for Raw Bird Drumstick.
Hylia River is likely named after the goddess Hylia though it may be named after Lake Hylia which it ultimately feeds into.