That's because low water levels make it impossible for re-enactors to navigate their wooden Durham boats.
Organizers say a "pretty significant amount" of precipitation must fall to raise the levels in time, adding that where and when any snow or rain occurs are also important factors.
The National Weather Service says no major storms appear on the horizon.
A final decision on whether to cross the river will likely be made just before Christmas. But the other events planned that day - including Washington's speech rallying the troops - will still take place even if the crossing is modified or cancelled.
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George Washington and his troops might not be able to make their annual Christmas Day trip across the Delaware River between Pennsylvania and New Jersey.