According to the Department for the Environment, Food and Rural Affairs (DEFRA), non-native invasive species can prey on, compete with and displace native wildlife. The can spread disease and block waterways. They can completely alter the balance of ecology in a water system.
Fish populations can alter, and they can block up waterways which mean boat users have to take different routes. The financial costs can run into millions of pounds.
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James Watson who was arrested over the unsolved 1994 murder of schoolboy Rikki Neave claims to be in Portugal having skipped bail.
People have been wandering into the grounds trying to catch the cartoon monsters.