The amazon has several (many) very distinctive biotopes.
https://www.google.com/search?q=ama...ligKzgIGoAQ&ved=0CAcQ_AUoAQ&biw=1920&bih=1030
Here are some ideas.
Some areas of the amazon are slow moving and others fast. Some have plants and clear water, others are tea colored with only deadwood and driftwood, others are brown colored from the dirt. Substrates include sand, mud, rock and gravel. Also, overhead canopies can include branches and flowering plants.
Really, one can go crazy with all the options.