A percolation ditch, also called infiltration ditch, is a type of best management practice (BMP) used to manage stormwater runoff, prevent downstream flooding and erosion, and improve water quality in an adjacent river, stream, lake, or bay. It is a shallow excavated trench filled with gravel or crushed stone that is designed to infiltrate stormwater through permeable soils into the underground aquifer.[1]​.

A percolation trench is similar to a dry well, which is generally an excavated hole filled with gravel.[2] Another similar drainage structure is a French drain, which directs water away from a building's foundation, but is generally not designed to protect water quality.

Percolation trenches are often used to treat runoff from impervious surfaces, such as sidewalks and parking lots, at sites where limited space is available to manage stormwater. They are effective in treating stormwater only if the soil has sufficient porosity. To function properly, a trench must be designed with a pretreatment structure, such as a grass channel or swale, to capture sediment and prevent clogging the trench.[3]​ It may not be appropriate for sites where there is the potential for groundwater contamination, or where there is soil with a high clay content that could clog the trench.[4]​.