Republicans in Florida racially gerrymandered two key state senate districts to disenfranchise Black voters and skew results in the Tampa Bay area, a panel of judges has heard.

In one district, they took a small chunk of St Petersburg heavy with minority voters and added it to an area of Tampa in a different county, and across a 10-mile waterway, leaving the remainder of its electorate “artificially white”, the court was told.

Lawyers for the American Civil Liberties Union of Florida, representing voters at a four-day trial in Tampa last week, said the state’s defense that the waters of Tampa Bay made the new district contiguous was ridiculous, pointing out in the lawsuit that “manatees don’t vote”.

“These are cities on opposite sides of the bay and there’s no way to go directly between them,” Caroline McNamara, an ACLU staff attorney, said.

“You either have to go across 10 miles of open ocean at the mouth of Tampa Bay, or you have to cut through other districts in the area through the north end.”