Brandi, the silky effect comes from a slow shutter speed on a tripod. The slower the speed, the silkier the look. The only reason you would need a filter i.e. a neutral density filter is if your scene is too bright to get a slow shutter speed. First, try setting the ISO to a very low number. If you are shooting in the morning or evening, chances are that the light level is low enough to accommodate you. If in the mid-afternoon, it depends on where the falls are located. If in an area with deep shadows are falling on the falls, you probably will be okay. If in bright sunlight, you are going to need to dial down the ISO speed and still may need to add a neutral density filter to be able to slow your shutter speed down enough to get the effect. I would get one that cuts light by 2-3 stops at least. I am unfamiliar with the D3000 but it should allow you to make all the necessary changes.