Can I dispose of leaves and other yard waste in wetlands?

The immediate response is "no", and this is a common violation.  Leaves and other organic material naturally fall into ponds, streams and other wetland areas, but adding to that by manual effort risks nutrient and material loading above what wetlands can naturally break down.  The result will be degradation of the wetland, and over time, even destruction of the wetland that will no longer function as it did as a home for wildlife and wetland plants, a buffer for run-off and a filter for pollution.  Essex offers free disposal of lawn and garden waste at the Town Transfer Station.  Alternately, consider composting the waste well away from wetlands.  That compost can be a valuable addition to your lawn and gardens in the future.