Pembrokeshire has no large lakes or dams. Bosherston Lakes are the only semi-natural lakes we have over five acres. They are famous for their water lily flowers which are seen every summer. They are also famous for their otters. The water originates from wells rising from an underground reservoir. Bosherston Lakes was built by the Cawdor family between 1780 and 1860 as the centerpiece of their design to enhance their landscape.

The Llys-y-Fran reservoir supplies water for the whole of the county during the impoundment of the Afon Syfnwy. Llys y Fran was built between 1968 and 1972. The Rosebush reservoir is smaller and was built in the 1880s. It provides water for south Pembrokeshire

There are two rivers of the Cleddau: the Western Cleddau in the west and the Eastern Cleddau. They join together to form the Daugleddau estuary, which gives its name to the important port of Milford Haven. There are two parts to the River Cleddau. The eastern section originates at Cleddau Eye in the parish of Llanfair Nant y Gôf, 4 km south east of Fishguard. It flows south-west past Scleddau. The western branch at Penysgwarne originates in the parish of Llanreithan, and flows east to join the other branch. The Western Cleddau flows through Wolfscastle to Haverfordwest. There, at high tide, its effect on water height is seen.

The River Cleddau flows on the slopes of the Preseli Hills in Blaencleddau in the parish of Mynachlog-ddu, and flows south-west past Llawhaden. The tidal effect is seen near Canaston Bridge. Join the River Cleddau at Picton Point. The Cleddau estuary is deep and a good natural harbour for trade and ferries to Ireland. Oil tankers of 300,000 tonnes and more can also use it. Because of this, many oil refineries were built here.

The next largest river in Pembrokeshire is the River Gwaun. It measures about 10 miles (15 km) and originates on the western slopes of the Preseli hills, not far from Tavern-y-Bwlch and Foel Eryr. It flows in a westerly direction, passing Cwm Gwaun, Pontfaen, and Llanychâr. It reaches the sea at Fishguard and flows into Fishguard Bay, which is part of Cardigan Bay. The estuary forms an important port from which ferries sail to Rosslare in Ireland.

Next in size is the River Nevern which flows to the sea at Newport. The rivers Cuch, Teifi and Taff all cross our county boundary but also belong to Ceredigion or Carmarthenshire.

Other areas of Wales are more mountainous and therefore have more lakes and rivers. The largest natural lake is Llyn Tegid near Bala. Climate change has resulted in severe flooding around several rivers in recent years. The Conwy and Tywi rivers in particular are causing problems. The debate about how to improve the situation, protecting lives and property, is a long and complex one. It reflects similar discussions on many continents, but particularly in areas of Asia e.g. the Yangtze River in China, and the Red River in Vietnam. Our land use is very relevant to this problem and governments are legislating to prevent land drainage and forest felling.

Engineer Sir Evan Jones from Fishguard was responsible for work on the Severn Tunnel, Aswan Reservoir in Egypt and the 1km long causeway between Singapore and Johor which opened in 1924.