1.Cut oranges and lemon in half; slice thinly, reserving seeds. Tie seeds in muslin.
2.Combine fruit, muslin bag and the water in large saucepan; bring to the boil. Reduce heat; simmer, covered, 45 minutes. Add carrot; simmer, covered, about 15 minutes or until rind is soft. Discard muslin bag.
3.Measure fruit mixture, allow ¾ cup sugar for each cup of fruit mixture. Return fruit mixture and sugar to pan; stir over high heat, without boiling, until sugar dissolves. Bring to the boil; boil, uncovered, without stirring, 40 minutes or until marmalade gels when tested.
4.Pour hot marmalade into hot sterilised jars; seal immediately. Label and date jars when cold.