that is in the shader info for that texture. You could either use a water texture with no waves or modify the standard ones shader with waves to copy the shader of the one without waves. I would only go that route if the texture with the waves will only do.
Canal_sludge and a couple in that family just 'sit' there without motion. There are a few of them with differing colors/textures. They can be found in the 'misc_outdoor' group. Also, the same group contains some 'algae' textures that should be right at the top. None of them 'move'. I don't think the 'subpen...' family moves either, so that may be viable. Just slap a couple on neighboring brushes and see. Don't forget to use a 'bottom' texture though if it can be seen. More questions, just ask!