In a letter to Bath and North East Somerset Council, the trust claimed that Crest Nicholson's revised plans for a 28ha development, which could provide up to 3,000 homes, remain too tall and dense.
The trust argued that riverside buildings remaining at eight and nine storeys "will have a detrimental effect" on the historical landscape. It said the buildings would "fail to preserve or enhance either the character or the appearance of the city-wide conservation area".
The density of up to 100 homes per hectare "appears far too great in comparison to the city centre", the organisation added. It maintained that the number of smaller homes that are proposed could affect the "creation of a balanced community".
Crest Nicholson managing director Debbie Aplin said: "We held a public exhibition in July and height was an issue. We have reduced the nine and seven-storey buildings next to the listed bridge to six storeys. We feel that a decision needs to be made because we have done everything that we can do."
An English Heritage spokeswoman commented: "We are fully assessing the detailed application for this scheme. We expect to have given our formal advice to the local authority by early next month."
The plan is likely to go to committee towards the end of November.