Story highlights Silas and Eli Keslar, both 18 months old, drowned in an Arizona canal

Their mother was trying to fend of a bee when the stroller rolled away, police say

(CNN) Eighteen-month-old twins drowned after their mother tried to fend off a bee and let go of their stroller, which rolled into a canal, Arizona police said.

Alexis Keslar was walking with her twin sons, Silas and Eli Keslar, along a canal Friday when she tried to repel a bee, police in Yuma said.

"The stroller rolled away from her into the canal, with the boys belted in the seat," police said Monday.

Keslar went into the canal and tried to rescue her sons, authorities said, but was hampered by the steep sides of the canal, the depth of the water and the force of the current. The current washed the stroller away.

After Keslar got out of the canal, she called for help, police said.