Nowadays, wireless sensor networks (WSNs) are used in several applications such as environmental monitoring. When network size and data rate increase, congestion becomes as an important issue, especially when an emergency situation generates alarm messages in a specific area of the network. In this paper, we describe the pivot routing protocol named PiRAT, which avoids congested paths by using intermediate pivot nodes. Simulations show that PiRAT has better performance than previous protocols in terms of packet loss, end-to-end delay, congestion and node overload. Moreover, we show that the load-balancing ability of PiRAT allows it to benefit from nodes having independent low duty cycles.