The first grand natural feature which arrests attention in the most cursory examination of the map of Nicaragua is the Great Lake. This lake with an area of some three thousand square miles and a water-shed of about eight thousand square miles, is unique in the large proportion of its own area to that of its water-shed. A result of this large proportion of water surface to drainage area, at once evident, is the very gradual changes of level of the lake and their confinement within very narrow limits. The difference between the level of the lake at the close of an abnormally dry season and its level at the close of an abnormally wet season is not more than ten feet, and the usual annual fluctuation is about five feet. The next features that arrest attention are, first, the very narrow ribbon of land intervening between the western shore of the Lake and the Pacific, and second, the entire absence of lateral tributaries of any size to the upper half of the San Juan River. The river is in fact, as it was originally most aptly named, simply the "Desaguadero" or drain of the Lake. [Illustration: ENTRANCE TO HIGHLANDS--RIVER SAN JUAN. _Julius Bien & Co._] The length of this river is one hundred and twenty miles, from the Lake to the Caribbean Sea, and its total fall from one hundred to one hundred and ten feet. Nature has separated the river into two nearly equal divisions, presenting distinct and opposite characteristics. From Lake Nicaragua to the mouth of the Rio San Carlos, a distance of sixty-one miles, in which occur several rapids, the total descent is fifty feet, quite irregularly distributed however. The surface slopes of the river vary from as much as 83.38 inches per mile for a short distance at Castillo rapids, to only .90 inch per mile through the Agua Muerte, the dead water below the Machuca rapids. The average width of the river through this upper section is seven hundred feet, the minimum four hundred and twenty. In some parts of the Agua Muerte the depth varies from fifty to seventy-five feet. There are very few islands in this section of the river, the banks are covered with huge trees matted with vines, and throughout the lower half of the division, from Toro rapids to the mouth of the San Carlos, the river is confined between steep hills and mountains. [Illustration: UPPER CASTILLO--RIVER SAN JUAN. _Julius Bien & Co._] As a result of the absence of considerable tributaries already noted, the fluctuations of this portion of the river conform closely to those of the Lake, and consequently take place gradually and are limited in range. Below the Rio San Carlos the San Juan changes its character entirely. Its average width is twelve hundred and fifty feet, its bottom is sandy, there are numerous islands, and the slope of the river is almost uniformly one foot per mile.