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A common application of unattended sensor networks (WSN) is low data rate streaming from many scattered sensors to one or more sink nodes. To meet the stringent requirement of prolonged WSN lifetime, we introduce a new notion of statistical reliability for data streaming applications and propose several variants of stop-and-wait hop-by-hop ARQ with explicit and implicit ACKs. The energy-efficiency of the protocols are mathematically analyzed and compared. The analysis reveals that implicit ACKs should be applied with caution to prevent an "avalanche" of implicit ACK transmissions. It is further shown that a simple combined implicit/explicit ACK resolves the "avalanche" problem. Our proposal is further validated by simulation.