TOLEDO, Ohio (AP) — Ohio’s environmental regulators are investigating over a dozen recent farm manure spills that have seeped into waterways mainly in the western part of the state.

Most of the spills reported to Ohio Environmental Protection Agency over the past week have been linked to farmers putting livestock waste on frozen farm fields. Warmer temperatures and melting snow are now causing the manure to run off the fields and into ditches, creeks and rivers.

State lawmakers are debating whether to ban farmers in northwestern Ohio from spreading manure on frozen and rain-soaked fields. Supporters say the runoff from the frozen fields is contributing to the algae plaguing Lake Erie.

Ohio EPA Director Craig Butler says that so far there haven’t been any large-scale fish kills linked to the spills.