(Portland, OR)  --  The Portland Water Bureau says the cause of E. coli contamination that triggered a boil-water order in the city last week hasn't yet been found.  The notice was issued Friday and lifted Saturday morning.  Crews spent the day yesterday cleaning out two reservoirs on Mount Tabor, which were drained after water samples tested positive for E. coli.  Officials say the source of the bacteria is likely animal, rather than human.