The Rhine crisis of 1840 was a diplomatic crisis between the Kingdom of France and the German Confederation, caused by the demand by French minister Adolphe Thiers that the river Rhine be reinstated as France's border in the east, at a loss of some 32,000 km² (12,000 sq mi) of German territory.

The "Rhine River conflict" typically refers to the decades-long diplomatic and environmental struggle among the nations bordering the river (Switzerland, France, Germany, Luxembourg, and the Netherlands) over industrial pollution and water rights. For much of the 20th century, the Rhine was known as the "sewer of Europe" due to massive chemical runoff from the Sandoz and BASF factories. The conflict reached a boiling point in 1986 following the Sandoz chemical spill in Basel, which turned the river red and killed millions of fish downstream in Germany and the Netherlands. This disaster forced the bordering nations to move from conflict to cooperation, leading to the Rhine Action Programme and the strengthening of the International Commission for the Protection of the Rhine (ICPR). Today, the "conflict" has shifted toward climate change and water levels; during recent droughts, low water has sparked tensions over who gets priority for shipping vs. cooling nuclear power plants vs. agricultural use, highlighting that even a "recovered" river remains a flashpoint for international resource management.