Data cleansing sounds like something you could outsource, right? Mostly not the case. Someone from outside can help you but they don't understand your business, processes, etc. That's why organizations assign data owners that are accountable for cleansing, and owners recruit and appoint data stewards from within the organization.
Data Lake is a repository of data stored in raw format (CSV, JSON, XML, text, binary, documents, etc.), in contrast to a traditional (relational) Database that enforces strict predefined schema (where data is arranged in tables and columns).
Data Swamp is a Data Lake is so messy that it is unusable and does not allow you to find or get value from your data.