Erythropotamos

Infobox River
river_name=Erythropotamos
Luda reka (Луда река)
origin=Eastern Rhodope mountains
basin_country=Bulgaria, Greece
length=approximately 100 km
mouth_elevation=Ionian Sea
watershed=Ionian Sea

The Erythropotamos ( _el. Ερυθροπόταμος, meaning "red river"), Luda reka in Bulgaria ( _bg. Луда река, meaning "mad river") is a river that flows from south of Mega Dereio next to the Ivaylovgrad municipality in southern Bulgaria and northern Greek Thrace entirely in the Evros Prefecture. Its Turkish name was "Küzüldeli Su". It flows into the Maritsa (Evros River) near Didymoteicho.

The river begins in Greece in the western Evros Prefecture, it passes into Mega Dereio and through a remote road into Ivaylovgrad municipality in Bulgaria, through the villages of Gorno Lukovo and Dolno Lukovo (Upper and Lower Lukovo) and Siv Kladenets with a tributary known as the Byala reka ("white river"). The river reenters Greece and flows north of Protoklissi, the nearby villages include Paliouri and Sitochori.