Think about basic needs and where to find them...
Food, water, shelter. Food either from animals living in the water or drinking from it or plants growing along river bank.
Water...
Shelter in natural formations made by the water or built from sticks, branches, mud, etc. found along riverbanks.
As the civilization and society matures, the next step is to trade goods and supplies with other groups. The easiest way to trasport those goods is on the water. Where there are goods changing hands there is going to be banks and money changers, companies will form to ship and sell and buy, services like lodging food and entertainment will become available for all the people visiting to buy, sell, or deliver, and governments will be needed to protect everything. Tah Dah! You have a civilization that emerged and grew in that location because of the river that runs through it...