Their echolocation system can have difficulty picking up very gently-sloping coastlines.[10] This theory accounts for mass beaching hot spots such as Ocean Beach, Tasmania and Geographe Bay, Western Australia where the slope is about half a degree (approximately 8 m [26 ft] deep one km [0.62 mi] out to sea). The University of Western Australia Bioacoustics group proposes that repeated reflections between the surface and ocean bottom in gently sloping shallow water may attenuate sound so much that the echo is inaudible to the whales.[4] Stirred up sand as well as long-lived microbubbles formed by rain may further exacerbate the effect.