Very important for the city is the Maritsa River. It is the longest Bulgarian river and the biggest on the Balkan Peninsula – 524.6 km, of which 322 km are on the territory of Bulgaria. Until the second half of the 19^th century it was navigable.

Maritsa (Greek Έβρος, Modern Greek Euros, old Greek Hebros, Turkish Meriç, Merich). The river originates in the Marichini Lakes in the Mountain Rila, runs southeast through the Upper Thracian Plain and flows into the Aegean Sea.

The river valley is characterized with rich surface and underground flows. The upper stream includes the Rila part of the basin as well as Ihtiman Sredna Gora to railway station Belovo, and it runs entirely in the mountain. The middle stream of the river starts at Belovo and finishes at the end of the Harmali Gorge and includes most of the Upper Thracian Plain, The lower stream starts at Harmali Gorge and on the territory of Bulgaria finishes at Svilengrad, The Maritsa River has about 100 major tributaries, located almost symmetrically to the river. Some of them are Sazliyka, Topolnitsa, Vacha, Stryama, Chepelarska. The tributaries at the western part of the river valley are rich in water unlike those in the eastern part of the basin. There is a big potential of underground waters.

In the past the Maritsa River was navigable from Belovo down the stream. Besides Plovdiv there are many settlements located on its banks such as Dolna Banya, Kostenets, Belovo, Pazardzhik, Dimitrovgrad, Simeonovgrad, Harmanli. Lyubimets, Svilengrad, etc.

Maritsa is the largest river in Bulgaria and its debit is relatively constant. Its basin includes most of Southern Bulgaria, from Stara Planina to the Rhodopes and from Rila to Sakar. It has about 100 major tributaries, located almost symmetrically to the river. Some of the rivers flowing into it are Topolnitsa, Vacha, Stryama, Chepelarska, Arda and Tundzha.

The protected areas along the Maritsa River are habitats of many plants and animals such as black alder, white elm, golden willow, pygmy cormorant, whooper swan, great white egret, black stork, ground squirrel, otter, mouse-tailed dormouse, spur-thighed tortoise, Hermann's Tortoise, common and Balkan loach, bitterling, barbel, purple heron, marsh harrier, etc.

A project under the name “Visit Maritsa” is renewing the attempts from the 70s to make the river navigable within the city limits. The National Strategy for development of tourism discusses the possibility for construction of entertainment parks and hotel.