Lake Amistad offers visitors many interesting natural features to investigate. The river and lake canyons have shear cliffs dotted with caves. The colorful canyon walls range from deep grays to bright yellows and reds as ground water oxidation makes them look as if large paintbrushes have painted them. These limestone cliffs are also full of marine fossils of the Permian era, over 360 million years old. Corals, gastropods (snails), ammonites, and various bivalve fossils are common. The karst topography resulting from the erosion of this limestone contributes to a complex pattern of groundwater. Although Lake Amistad is the convergence of the Rio Grande, Devils, and Pecos rivers, there are also other water sources that contribute to lake waters.
At the Devils River, about 8 miles up river from Rough Canyon, Indian Springs cascades out of the cliffs and provides additional waters to the lake. The springs are visible at lower lake levels, however they disappear underwater when levels are nearing the full pool elevation of 1117 ft above sea level. This spring affects the water by "cooling" it, and changes the color of the normal lake waters to a brilliant blue.
Goodenough Springs is located along the Rio Grande. Prior to the inundation, Goodenough Springs welled out of the ground and turned a water wheel for power. The spring is now many feet under the water surface, but still "warms" the water temperature in the immediate area. The lake water near the springs is probably in the 50 F- 60 F range, as the springs are usually between 60-80 feet or more below the lake surface.
Limnology is the study of inland waters. It may include the study of wetlands, creeks, streams and marshes, but it most certainly includes the study of lakes and reservoirs (man-made lakes)...especially whopping big ones like Lake Amistad. Lake Amistad is a limnologist's dream. It is fed by 3 rivers and numerous springs. The rivers and springs all have different characteristics that mix in the lake, making it a very interesting body of water from the standpoint of water chemistry and the biological community.