NPS Ranger reported that the boats were tied loosely together leaving a gap between the two where victim fell.  

See attachment on vessel 1 for narrative from NPS Ranger who was the first on scene and handled the death investigation for more details:

The female party on the houseboat informed Rangers that her husband fell off of their pontoon boat while trying to side tie it to their houseboat.  

deceased and wife were cleaning the vessel which tired them both.  he went to tie the pontoon boat to his other boat when he slipped and fell into the water.  due to fatigue from washing the pontoon boat he could not pull himself onto the other vessel.  wife stated deceased had seen his cardiologist before the trip and he was told to slow down
Halls Crossing                