Despite having a sword now, Herbert is honestly really hesitant to just. Cut up the water and jump in after a drowning water spirit who Lapis might already be fighting with water right now. Would cutting the water disrupt the fight? Maybe! He has no clue how that works. At this moment, Lambert's idea sounds a lot more feasible.

So he actually does advance somewhat on the pond, sword in both hands, not right up to the edge but close enough to search, and try to find the specific object that stands out that Lambert mentioned.