The water resource development of the province is thus centred on artificial Thác Bà Lake, which was created for hydropower development. The lake has an area of and has 1,331 islands. The hill catchment has a varied ecology; an interesting feature in the catchment with its beautiful landscape is thousands of hills and islands which have caves like the Hum, Cau Cuoi and Bach Xa. There is also a temple on the banks of lake known as Thác Bà Temple. The site that the lake now lies in was the historic scene in 1285 AD during the Thu Vat Battle that took place under the command of Trần Nhật Duật against Mongolian invaders. Thác Bà Lake is now an ecological tourist centre with entertainment, mountain climbing and hiking facilities. The Mong Son Grotto, which housed the Yên Bái Party Committee during the anti-American resistance is located at the centre of this lake.