Every year between November and April, rivers flood Baures, a savanna region in the Bolivian Amazon. Such seasonal inundation would have rendered the natural landscape essentially uninhabitable for most, but indigenous peoples have found ways around it--constructing elevated fields, settlement mounds and causeways--for thousands of years. Now new evidence suggests that they may have even taken advantage of their watery environs. In a study published today in the journal Nature, University of Pennsylvania anthropologist Clark L. Erickson< reports that a network of low, zigzag structures of raised earth and ponds covering hundreds of square kilometers in Baures represents a pre-Columbian fishery.

The 20-to-50-centimeter-tall fish weirs, Erickson notes, cover the spawning sites of numerous fish species. In practice, the weirs would have guided fish to places where they could be easily collected. And artificial ponds maintained throughout the year would have enabled continuous access to fresh fish and drinking water. The pre-Columbian structures are similar to fish weirs used by locals today, but the older structures were permanent and more extensive than their modern counterparts, which are rebuilt each season. In fact, considering the complexity of the pre-Columbian network, Erickson suggests that the weirs and large causeways might also have been used to manage water in the region. "The earthworks could have extended the period of inundation by capturing the first rains and holding floodwaters into the dry season," he writes.

"Prior to the arrival of the Europeans, the Native Americans of this region applied their knowledge of hydrology, soils, ecology and agriculture to build a highly productive landscape," Erickson notes, estimating that building the roughly 1,500 linear kilometers of fish weirs in Baures would have required some 300,000 person-days of labor. "Although the native peoples were removed from the lands by the Spanish missionaries and by European-introduced epidemics, the abandoned earthworks still influence the vegetation, drainage and biodiversity of the region today." In fact, the pre-Columbian approach might better serve the regions modern inhabitants, a possibility that Erickson hopes to address soon with an experimental fish weir project. "Archaeology can contribute to the long-term study of environments," he adds. "And, I believe, provide models for sustainable development based on past uses of the land."