A more thorough explanation:

The Great Lakes rule is a provision in maritime law that allows an admiralty litigant to have a jury trial in a contract or tort action if the lawsuit arises from the operation of a commercial vessel on the Great Lakes or the navigable waters connecting them. This rule is stated in 28 USCA § 1873.

For example, if a shipping company is sued for breach of contract by a supplier who provided goods for a vessel operating on the Great Lakes, the shipping company may be entitled to a jury trial under the Great Lakes rule.

It's important to note that in admiralty claims, litigants do not have a constitutional or statutory right to a jury trial, except for cases that fall under the Great Lakes rule.