For risks to occur, however, fish would have to be consumed on a daily basis over a period of many years. Significant risks were observed for the other five sites, but all five were sewage effluent-dominated tributaries. A second phase of this study is underway to better define the degree of impact, assess temporal variation, and further identify sources of toxic chemicals. The park sites are included in this second phase. Although several state and Federal agencies, including park staff, periodically monitor the quality of the river s water, the monitoring is not done frequently enough to give managers a clear understanding of the Rio Grande s water quality.
Most studies provide only a snapshot view of the river.
The Big Bend River Watchers group was formed in August 1994 to conduct this sampling and analysis from Presidio through Boquillas Canyon. Although the park cannot directly affect the quantity and quality of the river upstream, the park will continue to monitor water flows and quality and to participate in the Texas Watch program. The park has also begun working with the Rio Grande Compact Commission and the IBWC to explore long-term strategies to ensure minimum flow levels and treaty compliance. Although the Rio Grande forms a political boundary between two nations, the river creates many ties. Human habitation concentrates along the river to take advantage of its life-sustaining waters.