I wouldn't worry about chemicals that much unless you live downstream from some sort of industrial area. Chances are that the worst chemicals in the creek are fertilizer run-off from somebodies lawn or maybe soap from somebody washing their car.
BTW, do you know what kind of wood it is? Certain types of trees can be harmful to fish and inverts if any sap is remaining.
BTW, do you know what kind of wood it is? Certain types of trees can be harmful to fish and inverts if any sap is remaining.