William Lewis Herndon, Lieutenant, U.S.N., Exploration of the Valley of the Amazon… (1853)
“ The channels on these rivers are frequently obstructed by grounded trees, striking one of which the boat would almost inevitably perish. It is safer on the broader Amazon. The Ucayali, as far as Sarayacu, averages half a mile of width, twenty feet of depth at its lowest stage, and three miles the hour of current. I fear that there is a place at the great bend of the river, just below Sarayacu, where there are islands with extensive sand-flats, that may form, at the lowest stage of the river, an obstruction to navigation for a vessel of greater draught than ten feet. ”
