Line your garden pond with 45-mil EPDM EPDM rubber is the only material ... but the version sold by roofing suppliers often contains fungicides that can harm plants or fish. Protect the liner with ...

as well as at least a 40-mil fish safe flexible liner like AquaArmor. Rigid pond liners, will eventually crack and limit the pump and filter options. The pump system is the heart of the backyard koi ...