From purpose and study: The principal objectives of this study were as follows: (1) to determine the existing water-quality conditions in Lago Loiza as reflected by the principal chemical, physical, biological and bacteriological characteristics in the lake and its tributaries. (2) To estimate the reservoir's water budget during the study period, including the contributions from the tributaries and other sources. (3) Estimation of the reservoir's overall nitrogen and phosphorus budget, including the principal sources and sinks of these nutrients. (4) Definition of the sedimentation rate in the reservoir.