In addition to these, there are a number of large rivers which belong entirely to the plains in the northern and south-eastern portions of the island, the principal of which are the Arive and the Moderegam, which flow into the Gulf of Manaar; the Kala-oya and the Kanda-lady, which empty themselves into the Bay of Calpentyn; the Maniek or Kattragam, and the Koombookgam, opposite to the Little Bass rocks and the Naveloor, the Chadawak, and Arookgam, south of Batticaloa. The extent of country drained by these latter streams is little short of thirteen thousand square miles. Very few of the rivers of Ceylon are navigable, and these only by canoes and flat-bottomed paddy boats, which ascend some of the largest for short distances, till impeded by the rapids, occasioned by rocks in the lowest range of the hills. In this way the Niwalle at Matura can be ascended for about fifteen miles, as far as Wellehara; the Kalu-ganga can be traversed from Caltura to Ratnapoora; the Bentotte river for sixteen miles to Pittagalla; and the Kalany from Colombo to the foot of the mountains near Ambogammoa. The Mahawelli-ganga is navigable from Trincomalie to within a short distance of Kanda[1]; and many of the lesser streams, the Kirinde and Wellawey in the south, and the Kaymel, the Dedroo-oya, and the Aripo river on the west of the island, are used for short distances by boats. [Footnote 1: For an account of the capabilities of the Mahawelli-ganga, as regards navigation, see BROOKE'S _Report, Roy. Geog. Journ._ vol. iii. p. 223. and _post_, Vol. II. p. 423.] All these streams are liable, during the fury of the monsoons, to be surcharged with rain till they overflow their banks, and spread in wide inundations over the level country. On the subsidence of these waters, the intense heat of the sun acting on the surface they leave deserted, produces a noxious and fatal malaria. Hence the rivers of Ceylon present the curious anomaly, that whilst the tanks and reservoirs of the interior diffuse a healthful coolness around, the running water of the rivers is prolific of fevers; and in some seasons so deadly is the pestilence that the Malabar coolies, as well as the native peasantry, betake themselves to precipitate flight.[1] [Footnote 1: It has been remarked along the Mahawelli-ganga, a few miles from Kandy, that during the deadly season, after the subsidence of the rains, the jungle fever generally attacks one face of the hills through which it winds, leading the opposite side entirely exempted, as if the poisonous vapour, being carried by the current of air, affected only those aspects against which it directly impinged.]