The process of constructing a tram line down Sydney's oldest street and to the eastern suburbs was always going to present unexpected challenges.

But the requirement to build a dam, sufficient to meet the state's exacting dam safety standards, was probably not high on any list of possibilities.

Along the southern edge of Centennial Park, contractors are this year expending significant resources to ensure that what is now considered a dam will not be a threat to safety.

The dam is not a new body of water. Instead, the existing Centennial Park Pond has, because of the light rail project, become a dam.