From the 1st millennium B.C. through the 9th-century A.D. Classic Maya collapse, non-urban populations grew exponentially, doubling every 408 years, in the twin-lake (Yaxha-Sacnab) basin. Sharply accelerated slopewash and colluviation, amplified in the Yaxha subbasin by urban construction, transferred nutrients plus calcareous, silty clay to both lakes. Except for the urban silt, colluvium appearing as lake sediments has a mean total P concentration close to that of basin soils. Eutrophication is not demonstrable and was probably impeded, even in less impacted lakes, by suspended Maya silt. Environmental strain, the product of accelerating agroengineering demand and sequestering of nutrients in colluvium developed too slowly to act as a servomechanism, damping population growth, at least until late Classic time. -- AATA