Jeremy Renner's estranged wife thinks his pool is a death trap for their 2-year-old daughter because he won't install a safety fence ... so she's fighting him in court over it.
Sonni Pacheco's attorney was in court Wednesday in L.A., and told the judge Jeremy's koi pond and pool lack protective fencing. Sonni's afraid little Ava could fall in and drown before Jeremy gets to her.
Renner's side doesn't think a fence is needed because his laser detection system will alarm him if Ava were to fall into the pool or the pond.
They're also fighting over social media -- Sonni's uncomfortable with Jeremy posting pics of Ava.
We're told the custody battle's gotten so hostile, with neither side budging ... the exes are now willing to go to trial.