 The diversion of the Afon Glaslyn caused it to scour out a new natural harbour which had a deep enough draught for small ocean-going sailing ships, and the first public wharves were built in 1825.Individual quarry companies followed, building a series of wharves along the shore almost as far as Borth-y-Gest, and slate was carted from Ffestiniog down to the quays along the Afon Dwyryd, then boated to Porthmadog for transfer to seagoing vessels.In the second half of the 19th-century Porthmadog was a flourishing port, its population expanding from 885 in 1821 to over 3,000 by 1861.