Use a dovetail jig with a straight bit and then round the corners over. You can find out more by checking out the Porter Cable 4212 Dovetail Jig user's manual and supplemental manual. Page 26 in the...
Use popsickle sticks, elastic bands, electrical wire, plastic wrap and tape, i did it for a project in science class and it works well if you don't need anything to fancy. you can also take a look at...
Opinion as to what to classify it as and in general its size.
For example - what would be classed as a stream in USA might be bigger that the biggest 'river' in another country.