WASHINGTON — Two adults and two children are in the hospital after D.C. firefighters found high levels of carbon monoxide Sunday morning at an apartment in Northeast.

The adults were treated for elevated levels of carbon monoxide, and the children were transported to the hospital as a precaution.

The levels have dropped, as firefighters ventilated the unit and continue to monitor the readings.

The source of the carbon monoxide leak was the water heater, D.C. Fire said.

The apartment is on the 700 block of 51st Street Northeast.

WTOP’s Sae Robinson contributed to this report.