The largest lake in the province is Indawgyi in the Myitkyina district. It has an area of nearly 100 sq. m. and is surrounded on three sides by ranges of hills, but is open to the north where it has an outlet in the Indaw river. In the highlands of the Shan hills there are the Inle lakes near Yawnghwe, and in the Katha district also there is another Indaw which covers some 60 sq. m. Other lakes are the Paunglin lake in Minbu district, the Inma lake in Prome, the Tu and Duya in Henzada, the Shahkègyi and the Inyègyi in Bassein, the sacred lake at Ye in Tenasserim, and the Nagamauk, Panzemyaung and Walonbyan in Arakan. The Meiktila lake covers an area of some 5 sq. m., but it is to some extent at least an artificial reservoir. In the heart of the delta numerous large lakes or marshes abounding in fish are formed by the overflow of the Irrawaddy river during the rainy season, but these either assume very diminutive proportions or disappear altogether in the dry season.
The climate of the delta is cooler and more temperate than in Upper Burma, and this is shown in the fairer complexion and stouter physique of the people of the lower province as compared with the inhabitants of the drier and hotter upper districts as far as Bhamo, where there is a great infusion of other types of the Tibeto-Burman family. North of the apex of the delta and the boundary between the deltaic and inland tracts, the rainfall gradually lessens as far as Minbu, where what was formerly called the rainless zone commences and extends as far as Katha. The rainfall in the coast districts varies from about 200 in. in the Arakan and Tenasserim divisions to an average of 90 in Rangoon and the adjoining portion of the Irrawaddy delta. In the extreme north of Upper Burma the rainfall is rather less than in the country adjoining Rangoon, and in the dry zone the annual average falls as low as 20 and 30 in.
The temperature varies almost as much as the rainfall. It is highest in the central zone, the mean of the maximum readings in such districts as Magwe, Myingyan, Kyauksè, Mandalay and Shwebo in the month of May being close on 100° F., while in the littoral and sub-montane districts it is nearly ten degrees less. The mean of the minimum readings in December in the central zone districts is a few degrees under 60° F. and in the littoral districts a few degrees over that figure. In the hilly district of Mogôk (Ruby Mines) the December mean minimum is 36.8° and the mean maximum 79°. The climate of the Chin and Kachin hills and also of the Shan States is temperate. In the shade and off the ground the thermometer rarely rises above 80° F. or falls below 25° F. In the hot season and in the sun as much as 150° F. is registered, and on the grass in the cold weather ten degrees of frost are not uncommon. Snow is seldom seen either in the Chin or Shan hills, but there are snow-clad ranges in the extreme north of the Kachin country.
In the narrow valleys of the Shan hills, and especially in the Salween valley, the shade maximum reaches 100° F. regularly for several weeks in April. The rainfall in the hills varies very considerably, but seems to range from about 60 in. in the broader valleys to about 300 in. on the higher forest-clad ranges.