sentences:  The largest two of these, which enter the lake on its north-western and eastern shores, can be followed for over ¼ mile to the upper edges of the basin, even during drier periods.The heads of these two streams, where the damp ground produces an identifiable flow - at SH774465 on the slopes of Bryn y Bedol, and at SH783467 on the slopes of Pen y Bedw - should perhaps more correctly be regarded as the uppermost sources of the river Conwy.A small parapet with a sluice-gate, hardly worthy of the word "dam", controls the outflow from the southern end of the lake, the level of which has not changed since the early 19th century Ordnance Survey.