We present Adaptive Stream Detection, a simple technique for modulating the aggressiveness of a stream prefetcher to match a workload?s observed spatial locality. We use this concept to design a prefetcher that resides on an on-chip memory controller. The result is a prefetcher with small hardware costs that can exploit workloads with low amounts of spatial locality. Using highly accurate simulators for the IBM Power5+, we show that this prefetcher improves performance of the SPEC2006fp benchmarks by an average of 32.7% when compared against a Power5+ that performs no prefetching. On a set of 5 commercial benchmarks that have low spatial locality, this prefetcher improves performance by an average of 15.1%. When compared against a typical Power5+ that does perform processor-side prefetching, the average performance improvement of these benchmark suites is 10.2% and 8.4%. We also evaluate the power and energy impact of our technique. For the same benchmark suites, DRAM power consumption increases by less than 3%, while energy usage decreases by 9.8% and 8.2%, respectively. Moreover, the power consumption of the prefetcher itself is low; it is estimated to increase the power consumption of the Power5+ chip by 0.06%.