Swimmers have to rely on a good deal of power and torque generation in their entire body, as well as the stamina to go the distance against the resistance of the water. In that aspect they benefit from both the systemic energy use associated with long distance events, but also the power and explosivity one would expect from most skill sports.
Beta-Alanine and L-Citrulline are two products known to reduce time to exhaustion in exactly these kinds of event.
L-Carnitine for a better use of systemic energy resources.
L-Leucine is a muscle supporting amino acid.
Creatine is used for acceleration and power generation on the swimming strokes.
Mass Gainer and Gainer Oats provide energy and protein. They are an easy to digest fix.