yes i got the same objections before .BUT you are missing that the waterfall water has to be directed away from the skimmer by means of the rock i drew at the meeting of the stream and the pond. that water has to be sent opposite of the skimmer . that way you get the pond circulating and the clean water pushes the dirty toward the skimmer.
now if your stream came in where i wrote jet then i would leave the skimmer where you originally had in but your pond being long and narrow with the falls/ stream in the middle you'll have filtered water get sucked back into the filter before the dirty water gets a chance.
now if your stream came in where i wrote jet then i would leave the skimmer where you originally had in but your pond being long and narrow with the falls/ stream in the middle you'll have filtered water get sucked back into the filter before the dirty water gets a chance.