Leptopel, the colloidally or otherwise finely particulate organic and inorganic detritus suspended in natural bodies of water, varies in chemical composition and in relative quantities with reference to depth, latitude and proximity to land. The leptopelic material may be quantitatively recovered by passing the water through an ultrafilter of inert, insoluble adsorptiv.e powder. Apparatus has been designed to so recover such samples in situ at various depths.