A river near Caernarfon has been described as one of the best in the UK for rare plants, according to a new study.

Natural Resources Wales (NRW) says plant life in the Afon Gwyrfai is "thriving" after large submerged beds of varied species were discovered in five locations along the river.

They included floating water plantain - a rare and protected species of international importants - and in one area, the plants were even recorded producing seed, a rare sight in Britain.

The NRW survey councluded the special area of conversation (SAC) around the Afon Gwyrfai and Llyn Cwellyn was supporting healthy and diverse plant communities and meeting its population targets for a protected site.

Francesca Sanchez, a specialist advisor for freshwater habitat and species, said: "This is a strong result. The findings show that the Afon Gwyrfai remains one of the best examples in the UK for this kind of plant community."

"They play a vital role in supporting the river’s health by providing essential habitat for fish, invertebrates and other wildlife, which helps to sustain biodiversity. They also contribute to improving water quality by absorbing nutrients, trapping sediments and stabilising riverbeds.”

Such was the strength of the findings, some of the seeds were collected to contribute to the Millennium Seed Bank at London's Kew Gardens to help protect the species for the future.

The study focused on aquatic plant communities that are typical of clean, nutrient-poor rivers - such as water crowfoots, water-starworts and milfoils.

It was found the Gwyrfai also supported a range of mosses and other water plants that are key to the river's ecosystem.

But concerns were raised about 'early signs of pressure' at one location in the survey, where higher levels of filamentous algae was found, which could be linked to increased nutients in the water.

An NRW spokesperson said: "While the site still meets its targets for plant communities, it has been identified as at risk and will be investigated further."

"NRW has a dedicated project that is already working to maintain and improve water quality in the Gwyrfai. The study will be one element of a comprehensive condition assessment of the Afon Gwyrfai and Llyn Cwellyn SAC."

"Condition assessments provide a comprehensive understanding of the health of SACs and guide ongoing work to protect and improve the most valuable habitats in Wales."