(Gresham, OR)  --  A 15-year-old boy is dead after drowning in the Sandy River at Oxbow Park.  Police say the boy's family called 9-1-1 yesterday afternoon after he disappeared under the water's surface while swimming.  Crews recovered his body around 7 p.m.  It's the second time a child has drowned at the park in less than a month.  A 7-year-old boy died after drowning in the river two weeks ago today.  Gresham Fire officials are reminding swimmers to always wear a lifejacket in rivers and other waterways.