A microprocessor has a plurality of stream prefetch engines for prefetching a respective data stream from the system memory into the microprocessor cache memory and an instruction decoder that decodes instructions of the microprocessor instruction set. The instruction set includes a stream prefetch instruction that returns an identifier uniquely associating a data stream specified by the instruction with one of the engines. The instruction set also includes an explicit prefetch-triggering load instruction that specifies a stream identifier returned by a previously executed stream prefetch instruction. When the decoder decodes a conventional load instruction it does not prefetch; however, when it decodes an explicit prefetch-triggering load instruction it commences prefetching the specified data stream. In one embodiment, an indicator of the load instruction may explicitly specify non-prefetch-triggering. In another embodiment one stream prefetch engine is implicitly associated and the other engines are explicitly associated by the returned identifier.