Course The Tundzha springs at an altitude of 2,083 m some 250 m south of the summit of Yurushka Gramada (2,136 m) in the central
Balkan Mountains. Its source lies about two kilometers east of
Botev Peak (2,376 m), the highest summit in the mountain range. It flows south in a deep valley with steep slopes and a large longitudinal gradient. The riverbed is rocky with gravels. Its water current is high, reaching velocity of 1.5–2 m/s. The gorge is narrow, reaching some 100–200 m, with steep bare slopes and rocky uneven riverbed. There is a small widening of 0.8–1 km between the villages of
Srem and
Ustrem, after which the gorge narrows again with deforested slopes and in places almost canyon-like. In that section the river is about 60 m wide with an average depth of 1–2 m. Shortly after exiting the gorge the river forms the
Bulgaria–Turkey border for about 10 km. East of the village of
Matochina the Tundzha leaves Bulgaria and enters Turkey, where it flows into the Maritsa at an altitude of 32 m in the city of
Edirne. The annual distribution of Tundzha river discharge is determined by seasonal changes that characteristic of its basin's location in the transitional zone between the
temperate continental climatic zone and the
continental Mediterranean zone — generally high temperatures, short duration of snow cover in winter for the lowland areas and retention of relatively stable snow cover in winter in the mountainous parts of the basin, irregular distribution of rain with a peak in spring and a dry period with little rainfall in summer and autumn. In the western part of the Balkan Mountains, at the town of Kalofer, high water occurs in March–April, when spring rains overlap with snowmelt of the snow cover at higher altitudes above 1500–1700 m; low water begins in July. In the lower part of the catchment area the high water period shifts to winter or autumn, while the low water period begins one or two months earlier, in May or June. The average annual discharge is 0.47 m3/s at Kalofer, 33.5 m3/s at Elhovo and 39.7 m3/s at the Bulgaria–Turkey border. The average annual rainfall within the catchment basin is 550 mm; the average altitude of the basin 386 m; the density of the river network varies between 0.23 and 0.66 km/km2. == Ecology ==