Recent satellite photos indicate North Korea has repaired flood damage at its nuclear test facility and could conduct a quick atomic explosion if it chose.
But analysis provided by the 38 North website also shows water streaming out of a test tunnel that may cause problems.
Washington and others are pushing for UN sanctions in response to North Korea's successful long-range rocket launch on December 12 that outsiders consider a cover for a banned ballistic missile test.
But there is worry that Pyongyang may respond to punishment by conducting its third nuclear test.
The analysis of GeoEye and Digital Globe satellite photos from December 13 and earlier was conducted by 38 North, the website for the US-Korea Institute at Johns Hopkins School of Advanced International Studies.