Alexandria and Richmond both had waterways.

Both seemed covered by the executive action of the Proclamation in a state that was not completely covered by it.
Those 20,000 slaves were freed immediately by the Emancipation Proclamation."[24] This Union-occupied zone where freedom began at once included parts of eastern North Carolina, the Mississippi Valley, northern Alabama, the Shenandoah Valley of Virginia, a large part of Arkansas, and the Sea Islands of Georgia and South Carolina.[77] Although some counties of Union-occupied Virginia were exempted from the Proclamation, the lower Shenandoah Valley, and the area around Alexandria were covered.[24] Emancipation was immediately enforced as Union soldiers advanced into the Confederacy. Slaves fled their masters and were often assisted by Union soldiers