The phrase "be too deep" can be replaced with various synonyms depending on the context. If you mean an intense emotional state, the synonyms could include "be overwhelmed," "be consumed," or "be submerged." If you're referring to something that is too difficult to understand or too complicated, possible synonyms could be "be too inscrutable," "be too complex," or "be too abstract." In a physical sense, if something is too deep, it could be described as "be bottomless," "be unmeasurable," or "be impenetrable." It's important to choose the right synonym to achieve the intended meaning and effect of the sentence.