Determination of pollen concentration (absolute pollen frequency), combined with eight radiocarbon dates from a 16-m core, provides an estimate of pollen influx to a small lake in the present Big Woods area of south-central Minnesota. The observed variation in pollen influx is difficult to relate to the vegetational history inferred from the relative pollen stratigraphy. An alternative hypothesis relates the changes in pollen influx to variation in the water level and movement of sediment in the lake basin. The pollen stratigraphy is consistent with other sites in Minnesota and South Dakota; it indicates that the Rutz Lake area was covered by boreal forest at the time the lake was formed and by a parkland of deciduous trees shortly after. Prairie dominated the area from about 8000 to 3200 years ago, when an increase in moisture favored an oak parkland again. The remaining openings were invaded by the mixed deciduous forest known as the Big Woods about 400 years ago. An index of the charcoal content of the sediment is maximum during the time of greatest prairie expansion and confirms the importance of fire in the prairie environment.