DEQ was established by the Oregon Legislative Assembly in 1969 when it dissolved its predecessor, the Oregon State Sanitary Authority, which was created in 1938 in response to public outcry for cleanup of the Willamette River.
The establishment of DEQ in 1969 was a consequence of the Oregon Legislative Assembly's decision to discontinue its earlier agency, the Oregon State Sanitary Authority, which had been created in 1938 following widespread public outcry over the condition of the Willamette River.