Magic is used just as freely in the worlds as we use electricity in most parts of contemporary Australia. Magic is used to complete all kinds of large and small tasks. Most of the peoples (and much of the flora & fauna) are magical/can use magic but it is something that must be replenished from appropriate sources. The River is the primary source of all magic and can be accessed by the peoples through many things grown using water (most food, wine etc), however these secondary sources vary in strength and duration.
Certain magics are stronger/work better when on each of the world creatures, and certain magics cannot be performed in certain places because of this. Due to the impact of the world creatures routes and how this changes available water reserves, access to water & magic is very precious and is not always guaranteed on Uttie, Taeamor, Tael & Vespur.
Using magic is fuelled by emotion and intention. Anyone can attempt anything but culture and training (ie. access) makes a magic user more powerful and accurate.
There are very strict rules agreed by all the worlds around certain kinds of magic (killing for example) but the actual interpretations and implementation of these rules varies wildly between worlds.
The use of certain magics is known to harm the world-creatures and pollute the river. These magics are absolutely forbidden.